Method and apparatus for initiating radio resource control (RRC) connection for vehicle-to-everything (V2X) communication

ABSTRACT

A communication method and system for converging a 5th generation (5G) communication system for supporting higher data rates beyond a 4th generation (4G) system with a technology for Internet of things (IoT) are provided. The communication method and system include intelligent services based on the 5G communication technology and the IoT-related technology, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. A method of a user equipment (UE) for performing a vehicle-to-everything (V2X) sidelink communication is provided.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of prior application Ser.No. 16/831,275, filed on Mar. 26, 2020, which has issued as U.S. Pat.No. 11,206,712 on Dec. 21, 2021, which is based on and claimed priorityunder 35 U.S.C. § 119 (e) of a U.S. Provisional application Ser. No.62/823,752, filed on Mar. 26, 2019, in the U.S. Patent and TrademarkOffice, of a U.S. Provisional application Ser. No. 62/824,637, filed onMar. 27, 2019, in the U.S. Patent and Trademark Office, and of a U.S.Provisional application Ser. No. 62/825,366, filed on Mar. 28, 2019, inthe U.S. Patent and Trademark Office, of the disclosure of each of whichis incorporated by reference herein in its entirety.

BACKGROUND 1. Field

The disclosure relates to a method for initiating radio resource control(RRC) connection for vehicle-to-everything (V2X) communication and amethod for handling resources for hybrid automatic repeat request (HARQ)retransmission in V2X sidelink communication.

2. Description of Related Art

To meet the demand for wireless data traffic having increased sincedeployment of 4th generation (4G) communication systems, efforts havebeen made to develop an improved 5^(th) generation (5G) or pre-5Gcommunication system. Therefore, the 5G or pre-5G communication systemis also called a ‘beyond 4G network’ or a ‘post long term evolution(LTE) System.’ The 5G wireless communication system is considered to beimplemented not only in lower frequency bands but also in higherfrequency (mmWave) bands, e.g., 10 GHz to 100 GHz bands, so as toaccomplish higher data rates. To mitigate propagation loss of the radiowaves and increase the transmission distance, beamforming, massivemultiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO),array antenna, analog beam forming, and large-scale antenna techniquesare being considered in the design of the 5G wireless communicationsystem. In addition, in 5G communication systems, development for systemnetwork improvement is under-way based on advanced small cells, cloudradio access networks (RANs), ultra-dense networks, device-to-device(D2D) communication, wireless backhaul, moving network, cooperativecommunication, coordinated multi-points (CoMP), reception-endinterference cancellation, and the like. In the 5G system, frequency andquadrature amplitude modulation (FQAM), which is a combination of hybridfrequency shift keying (FSK) and quadrature amplitude modulation (QAM),and sliding window superposition coding (SWSC) as an advanced codingmodulation (ACM), filter bank multi-carrier (FBMC), non-orthogonalmultiple access (NOMA), and sparse code multiple access (SCMA) as anadvanced access technology, have been also developed.

In a similar regard, the Internet, which is a human centeredconnectivity network where humans generate and consume information, isnow evolving to the internet of things (IoT) where distributed entities,such as things, exchange and process information without humanintervention. The internet of everything (IoE), which is a combinationof IoT technology and big data processing technology through connectionwith a cloud server, has also emerged. As technology elements, such as“sensing technology,” “wired/wireless communication and networkinfrastructure,” “service interface technology,” and “securitytechnology” have been demanded for IoT implementation, a sensor network,a machine-to-machine (M2M) communication, machine-type communication(MTC), and so forth have been recently researched. Such an IoTenvironment may provide intelligent Internet technology services thatcreate a new value to human life by collecting and analyzing datagenerated among connected things. In this case, IoT may be applied to avariety of fields including a smart home, a smart building, a smartcity, a smart car or connected cars, a smart grid, health care, smartappliances, and advanced medical services through convergence andcombination between existing information technology (IT) and variousindustrial applications.

In line with this, various attempts have been made to apply 5Gcommunication systems to IoT networks. For example, technologies, suchas a sensor network, MTC, and M2M communication may be implemented bybeamforming, MIMO, and array antennas. Application of a cloud RAN as theabove-described big data processing technology may also be considered tobe as an example of convergence between the 5G technology and the IoTtechnology.

In recent years, several broadband wireless technologies have beendeveloped to meet the growing number of broadband subscribers and toprovide more and better applications and services such as these. Thesecond generation (2G) wireless communication system has been developedto provide voice services while ensuring the mobility of users. Thirdgeneration (3G) wireless communication system supports the voice serviceand data service. The 4G wireless communication system has beendeveloped to provide high-speed data service. However, the 4G wirelesscommunication system currently suffers from lack of resources to meetthe growing demand for high speed data services. Therefore, the 5Gwireless communication system is being developed to meet the growingdemand of various services with diverse requirements, e.g., high-speeddata services, support ultra-reliability and low-latency applications.

In addition, the 5G wireless communication system is expected to addressdifferent use cases having quite different requirements in terms of datarate, latency, reliability, mobility etc. However, it is expected thatthe design of the air-interface of the 5G wireless communication systemwill be flexible enough to serve user equipments (UEs) having quitedifferent capabilities depending on the use case and market segment inwhich the UE caters service to the end customer. Example use cases the5G wireless communication system is expected to address includesenhanced mobile broadband (eMBB), massive machine type communication(m-MTC), ultra-reliable low-latency communication (URLL), etc. The eMBBrequirements (e.g. tens of Gbps data rate, low-latency, high-mobility,and so on) address the market segment representing the wirelessbroadband subscribers needing internet connectivity everywhere, all thetime and on the go. The m-MTC requirements (e.g., very high connectiondensity, infrequent data transmission, very long battery life, lowmobility address and so on) address the market segment representing theIoT/IoE envisioning connectivity of billions of devices. The URLLrequirements (e.g., very low latency, very high reliability variablemobility, and so forth) address the market segment representing theIndustrial automation application andvehicle-to-vehicle/vehicle-to-infrastructure communication that isforeseen as one of the enablers for autonomous cars.

Vehicular communication services, represented by vehicle-to-everything(V2X) services, can include vehicle-to-vehicle (V2V),vehicle-to-infrastructure (V2I), vehicle-to-network (V2N) andvehicle-to-pedestrian (V2P) types. V2X services can be provided by PC5interface and/or Uu interface. Support of V2X services via PC5 interfaceis provided by V2X sidelink communication, which is a mode ofcommunication whereby UEs can communicate with each other directly overthe PC5 interface, and is supported when the UE is served by nextgeneration radio access network (NG-RAN) and when the UE is outside ofNG-RAN coverage. Only the UEs authorized to be used for V2X services canperform V2X sidelink communication.

The UE supporting V2X sidelink communication can operate in two modesfor resource allocation:

(1) Scheduled resource allocation (also referred as mode 1), in which:

The UE needs to be radio resource control connected (RRC_CONNECTED) inorder to transmit data, and

The UE requests transmission resources from the next generation node B(gNB), which schedules transmission resources for transmission ofsidelink control information and data.

(2) UE autonomous resource selection (also referred as mode 2), inwhich:

The UE unilaterally selects resources from resource pools and performstransport format selection to transmit sidelink control information anddata, and

The UE performs sensing for (re)selection of sidelink resources.

Based on sensing results, the UE (re)selects some specific sidelinkresources and reserves multiple sidelink resources.

A UE is considered in-coverage on the carrier used for V2X sidelinkcommunication whenever it detects a cell on that carrier. If the UE thatis authorized for V2X sidelink communication is in-coverage on thefrequency used for V2X sidelink communication or if the gNB provides V2Xsidelink configuration for that frequency (including when the UE is outof coverage on that frequency), the UE uses the scheduled resourceallocation or UE autonomous resource selection as a per gNBconfiguration. When the UE is out of coverage on the frequency used forV2X sidelink communication and if the gNB does not provide V2X sidelinkconfiguration for that frequency, the UE may use a set of transmissionand reception resource pools pre-configured in the UE. V2X sidelinkcommunication resources are not shared with other non-V2X datatransmitted over the sidelink.

An RRC_CONNECTED UE may send a sidelink UE information message to theserving cell if it is interested in V2X sidelink communicationtransmission in order to request sidelink resources. If the UE isconfigured by upper layers to receive V2X sidelink communication and V2Xsidelink reception resource pools are provided, the UE receivescommunication on those provided resources.

For V2X sidelink communication, sidelink transmission and/or receptionresources including an exceptional pool for different frequencies forscheduled resource allocation and UE autonomous resource selection maybe provided. The sidelink resources for different frequencies can beprovided via dedicated signaling, system information block 21 (SIB21)and/or pre-configuration. The serving cell may indicate to the UE onlythe frequency on which the UE may acquire the resource configuration forV2X sidelink communication. If multiple frequencies and associatedresource information are provided, it is up to UE implementation toselect the frequency among the provided frequencies. The UE shall notuse preconfigured transmission resource if the UE detects a cellproviding resource configuration or inter-carrier resource configurationfor V2X sidelink communication. Frequencies which may provide V2Xsidelink communication resource configuration or cross-carrierconfiguration can be signaled in the SIB21 or pre-configured in the UE.The radio resource control idle (RRC_IDLE) UE may prioritize thefrequency that provides cross-carrier resource configuration for V2Xsidelink communication during cell reselection.

If the UE supports multiple transmission chains, it may simultaneouslytransmit on multiple carriers via PC5. When multiple frequencies for V2Xare supported, a mapping between V2X service types and V2X frequenciesis configured by upper layers. The UE should ensure a V2X service to betransmitted on the corresponding frequency. For scheduled resourceallocation, the gNB can schedule a V2X transmission on a frequency basedon the sidelink buffer status report (BSR), in which the UE includes thedestination index uniquely associated with a frequency reported by theUE to the gNB in a sidelink UE information message.

V2X sidelink communication technology was defined and is referred as LTEV2X sidelink communication in the 4G system. V2X sidelink communicationis being enhanced to support enhanced V2X use cases in the 5G system,which are broadly arranged into four use case groups:

1) Vehicles platooning enables the vehicles to dynamically form aplatoon travelling together. All the vehicles in the platoon obtaininformation from the leading vehicle to manage this platoon. Thisinformation allows the vehicles to drive closer than normal in acoordinated manner, going to the same direction and travelling together.

2) Extended sensors enable the exchange of raw or processed datagathered through local sensors or live video images among vehicles, roadsite units, devices of pedestrian and V2X application servers. Thevehicles can increase the perception of their environment beyond of whattheir own sensors can detect and have a more broad and holistic view ofthe local situation. High data rate is one of the key characteristics.

3) Advanced driving enables semi-automated or full-automated driving.Each vehicle and/or road side unit (RSU) shares its own perception dataobtained from its local sensors with vehicles in proximity and thatallows vehicles to synchronize and coordinate their trajectories ormaneuvers. Each vehicle shares its driving intention with vehicles inproximity too.

4) Remote driving enables a remote driver or a V2X application tooperate a remote vehicle for those passengers who cannot drive bythemselves or remote vehicles located in dangerous environments. For acase where variation is limited and routes are predictable, such aspublic transportation, driving based on cloud computing can be used.High reliability and low latency are the main requirements.

Issue 1: According to current sidelink design, if mode 2 or commontransmission (TX) resource pool(s) are configured in system information(e.g. V2X SIB) and UE is in RRC_IDLE or radio resource control inactive(RRC_INACTIVE) state, it has to use mode 2 or common TX resources. Mode1 (i.e. dedicated resources) are beneficial for latency sensitiveadvanced V2X use cases. In order to enable RRC_IDLE/INACTIVE UEs toobtain mode 1 (i.e. dedicated resources), network may not configure modeor common TX resource pool(s) in system information. However, this isnot an efficient approach as this will trigger all V2X UEs in RRC_IDLEor RRC_INACTIVE state and interested in V2X sidelink communication toinitiate RRC connection. So, an efficient method of initiatingconnection is needed.

Issue 2: There are two radio access technologies (RATs) for V2X sidelinkcommunication. LTE V2X sidelink communication supports broadcastcommunication and caters limited V2X use cases. New radio (NR) V2Xsidelink communication supports unicast/broadcast/groupcastcommunication for advanced V2X uses cases.

In NR system, following configurations are supported.

-   -   gNB (or NR Cell) can configure V2X sidelink communication        configuration for NR Sidelink    -   gNB (or NR Cell) can configure V2X sidelink communication        configuration for LTE Sidelink    -   gNB (or NR Cell) can configure V2X sidelink communication        configuration for LTE Sidelink and NR sidelink

Scenario 1: UE is camped on an NR Cell. It broadcasts transmissionresource pool(s) for V2X sidelink communication. The RAT correspondingto these resources is NR sidelink. V2X service which initiated sidelinkcommunication needs to use LTE sidelink. However, as per currentcondition, UE cannot initiate RRC connection as system informationbroadcasts transmission resource pool(s) for V2X sidelink communication.

Scenario 2: UE is camped on an NR Cell. It broadcasts transmissionresource pool(s) for V2X sidelink communication. The RAT correspondingto these resources is LTE sidelink. V2X service which initiated sidelinkcommunication needs to use NR sidelink. However, as per currentcondition, UE cannot initiate RRC connection as system informationbroadcasts transmission resource pool(s) for V2X sidelink communication.

Scenario 3: UE is camped on an NR Cell. It broadcasts transmissionresource pool(s) for V2X sidelink communication. The RAT correspondingto these resources is LTE sidelink or NR sidelink. V2X service whichinitiated sidelink communication needs to use NR sidelink as well as LTEsidelink. However, as per current condition, UE cannot initiate RRCconnection.

To overcome the above issues, a trigger to initiate RRC connection needsto be enhanced.

In addition, in NR V2X sidelink communication, HARQ feedback issupported for unicast and groupcast communication.

Scenario 4: Transmitter, i.e. TX UE is in coverage and gNB configuresmode 1 resource for transmission.

Basic Operation: UE transmits sidelink (SL) BSR to gNB. TX UE receivesphysical downlink control channel (PDCCH) addressed to SL V2X radionetwork temporary identifier (SL-V-RNTI) from gNB wherein downlinkcontrol information (DCI) indicates resource for SL transmission. UEgenerates the MAC protocol data unit (PDU). UE transmits physical SLcontrol channel (PSCCH). UE transmits SL transport block (TB) (incl. MACPDU) on physical SL shared channel (PSSCH). Reception (RX) UE sends SLHARQ feedback (HARQ-acknowledge (ACK) or HARQ-negative ACK (NACK)) onphysical SL feedback channel (PSFCH).

Issue 3: In case TX UE receives sidelink HARQ-NACK from RX UE, the issueis how to perform HARQ retransmission, e.g. how the TX UE obtainsresource for HARQ retransmission.

Issue 4: In LTE, V2X communication source layer-2 identifier (ID) isalways included in SL shared channel (SCH) MAC header of MAC PDU. NR V2Xsidelink communication supports unicast/groupcast/broadcastcommunication. NR V2X supports HARQ feedback for unicast/groupcast. HARQfeedback can be enabled/disabled. Considering the above characteristicsof NR V2X communication, it is not efficient to always include sourcelayer-2 ID in SL SCH MAC header. A method to determine whether toinclude source layer-2 ID in SL SCH MAC header or not is needed.

The above information is presented as background information only toassist with an understanding of the disclosure. No determination hasbeen made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the disclosure.

SUMMARY

Aspects of the disclosure are to address at least the above-mentionedproblems and/or disadvantages and to provide at least the advantagesdescribed below. Accordingly, an aspect of the disclosure is to providea communication method and system for converging a 5th generation (5G)communication system for supporting higher data rates beyond a 4thgeneration (4G) system.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiment.

In accordance with an aspect of the disclosure, a method of a userequipment (UE) for performing a vehicle-to-everything (V2X) sidelinkcommunication is provided. The method includes determining to transmit afirst radio access technology (RAT) V2X sidelink communication on afirst frequency, receiving, from a base station associated with a secondRAT on a second frequency, system information on the first RAT V2Xsidelink communication, in case that the first frequency corresponds tothe second frequency, identifying whether the system informationincludes transmission resources for the first RAT V2X sidelinkcommunication on the first frequency, in case that the systeminformation does not include the transmission resources for the firstRAT V2X sidelink communication on the first frequency, initiating aradio resource control (RRC) connection for the first RAT V2X sidelinkcommunication, transmitting, to the base station, a sidelink UEinformation message for the first RAT V2X sidelink communication uponestablishing the RRC connection, and receiving, from the base station,an RRC reconfiguration message including the transmission resources forthe first RAT V2X sidelink communication on the first frequency.

In accordance with another aspect of the disclosure, a user equipment(UE) for performing a V2X sidelink communication is provided. The UEincludes a transceiver and at least one processor operatively coupledwith the transceiver and configured to determine to transmit a first RATV2X sidelink communication on a first frequency, control the transceiverto receive, from a base station associated with a second RAT on a secondfrequency, system information on the first RAT V2X sidelinkcommunication, in case that the first frequency corresponds to thesecond frequency, identify whether the system information includestransmission resources for the first RAT V2X sidelink communication onthe first frequency, in case that the system information does notinclude the transmission resources for the first RAT V2X sidelinkcommunication on the first frequency, control the transceiver toinitiate an RRC connection for the first RAT V2X sidelink communication,control the transceiver to transmit, to the base station, a sidelink UEinformation message for the first RAT V2X sidelink communication uponestablishing the RRC connection, and control the transceiver to receive,from the base station, an RRC reconfiguration message including thetransmission resources for the first RAT V2X sidelink communication onthe first frequency.

In accordance with another aspect of the disclosure, a method of a basestation for performing a V2X sidelink communication is provided. Themethod includes transmitting, to a UE, system information on a first RATV2X sidelink communication based on a second RAT on a first frequency,wherein the UE is configured to transmit the first RAT V2X sidelinkcommunication on a second frequency, in case that the second frequencycorresponds to the first frequency and the system information does notinclude transmission resources for the first RAT V2X sidelinkcommunication on the second frequency, initiating an RRC connection forthe first RAT V2X sidelink communication, receiving, from the UE, asidelink UE information message for the first RAT V2X sidelinkcommunication upon establishing the RRC connection, and transmitting, tothe UE, an RRC reconfiguration message including the transmissionresources for the first RAT V2X sidelink communication on the secondfrequency.

In accordance with another aspect of the disclosure, a method of a basestation for performing a V2X sidelink communication is provided. Thebase station includes a transceiver and at least one processoroperatively coupled with the transceiver. The at least one processor isconfigured to control the transceiver to transmit, to a user equipment(UE), system information on a first radio access technology (RAT) V2Xsidelink communication based on a second RAT on a first frequency,wherein the UE is configured to transmit the first RAT V2X sidelinkcommunication on a second frequency, in case that the second frequencycorresponds to the first frequency and the system information does notinclude transmission resources for the first RAT V2X sidelinkcommunication on the second frequency, initiate a radio resource control(RRC) connection for the first RAT V2X sidelink communication, controlthe transceiver to receive, from the UE, a sidelink UE informationmessage for the first RAT V2X sidelink communication upon establishingthe RRC connection, and control the transceiver to transmit, to the UE,an RRC reconfiguration message including the transmission resources forthe first RAT V2X sidelink communication on the second frequency.

Other aspects, advantages, and salient features of the disclosure willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses various embodiments of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the disclosure will be more apparent from the followingdescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is an example illustration of a method according to an embodimentof the disclosure;

FIG. 2 is another example illustration of a method according to anembodiment of the disclosure;

FIG. 3 is another example illustration of a method according to anembodiment of the disclosure;

FIG. 4 is an example illustration of a method according to an embodimentof the disclosure;

FIG. 5 is another example illustration of a method according to anembodiment of the disclosure;

FIG. 6 illustrates a method for new radio (NR) connection initiationtriggers for vehicle-to-everything (V2X) sidelink communicationaccording to an embodiment of the disclosure;

FIG. 7 illustrates another method for NR connection initiation triggersfor V2X sidelink communication according to an embodiment of thedisclosure;

FIG. 8 illustrates another method for NR connection initiation triggersfor V2X sidelink communication according to an embodiment of thedisclosure;

FIG. 9 illustrates another method for NR connection initiation triggersfor V2X sidelink communication according to an embodiment of thedisclosure;

FIG. 10 illustrates a method for LTE connection initiation triggers forV2X sidelink communication according to an embodiment of the disclosure;

FIG. 11 illustrates another method for LTE connection initiationtriggers for V2X sidelink communication according to an embodiment ofthe disclosure;

FIG. 12 shows sidelink (SL) bandwidth part (BWP) and uplink (UL) BWPdepending on the configuration according to an embodiment of thedisclosure;

FIG. 13 shows an LTE sidelink media access control (MAC) protocol dataunit (PDU) format according to an embodiment of the disclosure;

FIG. 14 illustrates a source layer 2 transmission mechanism according toan embodiment of the disclosure;

FIG. 15 illustrates another source layer 2 transmission mechanismaccording to an embodiment of the disclosure;

FIG. 16 illustrates another source layer 2 transmission mechanismaccording to an embodiment of the disclosure;

FIGS. 17, 19, 20, 21, 22, 23 and 24 illustrate the timelines ofoperations for requesting SL grant for retransmission according tovarious embodiments of the disclosure;

FIG. 18 is the signaling flow between transmitter UE, receiver UE andgNB according to an embodiment of the disclosure;

FIGS. 25 and 26 are the signaling flows between UE and gNB for acquiringV2X SIB(s) according to embodiments of the disclosure;

FIG. 27 is a block diagram of a terminal according to an embodiment ofthe disclosure; and

FIG. 28 is a block diagram of a base station according to an embodimentof the disclosure.

Throughout the drawings, like reference numerals will be understood torefer to like parts, components, and structures.

DETAILED DESCRIPTION

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of variousembodiments of the disclosure as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding, but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the various embodiments describedherein can be made without departing from the scope and spirit of thedisclosure. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but are merely used to enable aclear and consistent understanding of the disclosure. Accordingly, itshould be apparent to those skilled in the art that the followingdescription of various embodiments of the disclosure is provided forillustration purpose only and not for the purpose of limiting thedisclosure as defined by the appended claims and their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

By the term “substantially” it is meant that the recited characteristic,parameter, or value need not be achieved exactly, but that deviations orvariations, including for example, tolerances, measurement error,measurement accuracy limitations and other factors known to those ofskill in the art, may occur in amounts that do not preclude the effectthe characteristic was intended to provide.

It is known to those skilled in the art that blocks of a flowchart (orsequence diagram) and a combination of flowcharts may be represented andexecuted by computer program instructions. These computer programinstructions may be loaded on a processor of a general purpose computer,special-purpose computer, or programmable data processing equipment.When the loaded program instructions are executed by the processor, theycreate a means for carrying out functions described in the flowchart.Because the computer program instructions may be stored in a computerreadable memory that is usable in a specialized computer or aprogrammable data processing equipment, it is also possible to createarticles of manufacture that carry out functions described in theflowchart. Because the computer program instructions may be loaded on acomputer or a programmable data processing equipment, when executed asprocesses, they may carry out operations of functions described in theflowchart.

A block of a flowchart may correspond to a module, a segment, or a codecontaining one or more executable instructions implementing one or morelogical functions, or may correspond to a part thereof. In some cases,functions described by blocks may be executed in an order different fromthe listed order. For example, two blocks listed in sequence may beexecuted at the same time or executed in reverse order.

In this description, the words “unit”, “module” or the like may refer toa software component or hardware component, such as, for example, afield-programmable gate array (FPGA) or an application-specificintegrated circuit (ASIC) capable of carrying out a function or anoperation. However, a “unit”, or the like, is not limited to hardware orsoftware. A unit, or the like, may be configured so as to reside in anaddressable storage medium or to drive one or more processors. Units, orthe like, may also refer to software components, object-orientedsoftware components, class components, task components, processes,functions, attributes, procedures, subroutines, program code segments,drivers, firmware, microcode, circuits, data, databases, datastructures, tables, arrays or variables. A function provided by acomponent and unit may be a combination of smaller components and units,and may be combined with others to compose larger components and units.Components and units may be configured to drive a device or one or moreprocessors in a secure multimedia card.

Prior to the detailed description, terms or definitions necessary tounderstand the disclosure are described. However, these terms should beconstrued in a non-limiting way.

A base station (BS) is an entity communicating with a user equipment(UE) and may be referred to as a BS, a base transceiver station (BTS), anode B (NB), an evolved NB (eNB), an access point (AP), a fifthgeneration (5G) NB (5GNB), or a next generation NB (gNB).

A UE is an entity communicating with a BS and may be referred to as aUE, a device, a mobile station (MS), a mobile equipment (ME), or aterminal.

Connection Initiation Triggers for Mode 1 Resource Allocation

According to current sidelink design, if one or more common transmission(TX) resource pool(s) are configured in system information (e.g.vehicle-to-everything (V2X) system information block (SIB)) and UE is inradio resource control idle (RRC_IDLE) or radio resource controlinactive (RRC_INACTIVE) state, it has to use mode 2 (also referred ascommon TX resources) transmission resources for V2X sidelinktransmission. Mode 1 (also referred as dedicated resources) transmissionresources are beneficial for latency sensitive advanced V2X use cases.In order to enable RRC_IDLE/INACTIVE UEs to obtain dedicatedtransmission resources, network may not configure common TX resourcepool(s) in system information. However, this is not an efficientapproach as this will trigger all V2X UEs in RRC_IDLE or RRC_INACTIVEstate and interested in V2X sidelink transmission to initiate RRCconnection.

In the RRC_IDLE and RRC_INACTIVE, UE has access to only mode 2 (i.e.common) transmission resource pool(s) configured via system information.So in order to enable UE to request and get configured with mode 1transmission resources, it is proposed that UE interested in V2Xsidelink transmission can initiate RRC connection even if mode 2transmission resources are broadcasted by the camped cell for thefrequency (serving or non-serving) on which the UE is configured totransmit new radio (NR) V2X sidelink communication.

In one method of this disclosure, it is proposed that:

-   -   UE camped on a cell in RRC_IDLE/INACTIVE state and interested in        mode 1 transmission resources, initiates an RRC connection, if        the frequency on which the UE is configured to transmit V2X        sidelink communication concerns the camped frequency and if the        system information (i.e. V2X SIB) received/acquired from the        camped cell includes V2X sidelink configuration for the camped        frequency.    -   UE camped on cell in RRC_IDLE/INACTIVE state and interested in        mode 1 transmission resources, initiates an RRC connection, if        the frequency on which the UE is configured to transmit V2X        sidelink communication is included in V2X inter-frequency        information list in system information (i.e. V2X SIB)        received/acquired from the camped cell.    -   UE camped on an NR cell in RRC_IDLE/INACTIVE state and        interested in mode 1 transmission resources for NR V2X sidelink        communication, initiates an RRC connection on the NR cell, if        the frequency on which the UE is configured to transmit NR V2X        sidelink communication concerns the camped frequency and if the        system information (i.e. V2X SIB) received/acquired from the        camped cell includes NR V2X sidelink configuration for the        camped frequency.    -   UE camped on an NR cell in RRC_IDLE/INACTIVE state and        interested in mode 1 transmission resources for NR V2X sidelink        communication, initiates an RRC connection on the NR cell, if        the frequency on which the UE is configured to transmit NR V2X        sidelink communication is included in V2X inter-frequency        information list in system information (i.e. V2X SIB)        received/acquired from the camped cell (i.e. NR cell).    -   UE camped on an long term evolution (LTE) cell in        RRC_IDLE/INACTIVE state and interested in mode 1 transmission        resources for NR V2X sidelink communication, initiates an RRC        connection on the LTE cell, if the frequency on which the UE is        configured to transmit NR V2X sidelink communication concerns        the camped frequency and if the system information (i.e. V2X        SIB) received/acquired from the camped cell (i.e. LTE cell)        includes NR V2X sidelink configuration for the camped frequency.    -   UE camped on an LTE cell in RRC_IDLE/INACTIVE state and        interested in mode 1 transmission resources for NR V2X sidelink        communication, initiates an RRC connection on the LTE cell, if        the frequency on which the UE is configured to transmit NR V2X        sidelink communication is included in V2X inter-frequency        information list in system information (i.e. V2X SIB)        received/acquired from the camped cell (i.e. LTE cell).

It is possible that camped cell may only support mode 2 transmissionresource configuration for camped frequency as well as for otherfrequencies. To avoid unnecessary connection initiation for mode 1transmission resources, it is also proposed that cell can indicate(common for all frequencies or individually for each frequency) whethermode 1 is supported or not in system information. In another method ofthis disclosure, it is proposed that:

-   -   UE camped on a cell in RRC_IDLE/INACTIVE state and interested in        mode 1 transmission resources, initiates an RRC connection, if        the frequency on which the UE is configured to transmit V2X        sidelink communication concerns the camped frequency and if the        system information (i.e. V2X SIB) received/acquired from the        camped cell includes V2X sidelink configuration for the camped        frequency and indicates that mode 1 transmission resources are        supported by the camped cell on the camped frequency.    -   UE camped on cell in RRC_IDLE/INACTIVE state and interested in        mode 1 transmission resources, initiates an RRC connection, if        the frequency on which the UE is configured to transmit V2X        sidelink communication is included in V2X inter-frequency        information list in system information (i.e. V2X SIB)        received/acquired from the camped cell and mode 1 transmission        resources for V2X sidelink communication are supported by the        camped cell on concerned frequency.    -   UE camped on an NR cell in RRC_IDLE/INACTIVE state and        interested in mode 1 transmission resources for NR V2X sidelink        communication, initiates an RRC connection on the NR cell, if        the frequency on which the UE is configured to transmit NR V2X        sidelink communication concerns the camped frequency and if the        system information (i.e. V2X SIB) received/acquired from the        camped cell (i.e. NR cell) includes NR V2X sidelink        configuration for the camped frequency and mode 1 transmission        resources for NR V2X sidelink communication are supported by the        camped cell on the camped frequency.    -   UE camped on an NR cell in RRC_IDLE/INACTIVE state and        interested in mode 1 transmission resources for NR V2X sidelink        communication, initiates an RRC connection on the NR cell, if        the frequency on which the UE is configured to transmit NR V2X        sidelink communication is included in V2X inter-frequency        information list in system information (i.e. V2X SIB)        received/acquired from the camped cell (i.e. NR cell) and mode 1        transmission resources for NR V2X sidelink communication are        supported by the camped cell on concerned frequency.    -   UE camped on an LTE cell in RRC_IDLE/INACTIVE state and        interested in mode 1 transmission resources for NR V2X sidelink        communication, initiates an RRC connection on the LTE cell, if        the frequency on which the UE is configured to transmit NR V2X        sidelink communication concerns the camped frequency (i.e.        frequency of the camped LTE cell) and if the system information        (i.e. V2X SIB) received/acquired from the camped cell includes        NR V2X sidelink configuration for the camped frequency and mode        1 transmission resources for NR V2X sidelink communication are        supported by the camped cell on the camped frequency.    -   UE camped on an LTE cell in RRC_IDLE/INACTIVE state and        interested in mode 1 transmission resources for NR V2X sidelink        communication, initiates an RRC connection on the LTE cell, if        the frequency on which the UE is configured to transmit NR V2X        sidelink communication is included in V2X inter-frequency        information list in system information (i.e. V2X SIB)        received/acquired from the camped cell (i.e. LTE cell) and mode        1 transmission resources for NR V2X sidelink communication are        supported by the camped cell on concerned frequency.

FIG. 1 is an example illustration of a method according to an embodimentof the disclosure.

Referring to FIG. 1 , UE is in RRC_IDLE/INACTIVE state and interested inV2X sidelink transmission on frequency F1. UE acquires the V2X SIB(s)transmitted by the camped cell at operation 110. The acquired V2X SIBincludes mode 2 transmission resource pool(s) for frequency F1. The V2XSIB also includes information indicating that the mode 1 transmissionresources are supported for frequency F1 (the indication Mode1Supportedlnd can be common for all V2X frequencies or individually foreach frequency). In an embodiment, Mode1 Supportedlnd indication can beConnectionAllowedInd or ConnectionAllowedforMode 1. Even though the mode2 transmission resource pool(s) for frequency F1 are included in V2XSIB, if the V2X sidelink transmission requires mode 1 transmissionresources and mode 1 transmission resources are supported on frequencyF1, UE initiates an RRC connection setup/resume procedure at operation120. In order to determine whether mode 1 transmission resources arerequired for V2X sidelink transmission or not, mapping between V2Xservices and mode1/mode 2 transmission resources can be(pre-)configured. After the RRC connection is setup at operation 120, UEtransmits sidelink UE information message to gNB/BS to indicate that itis interested in V2X sidelink transmission on frequency F1 and it needsmode 1 transmission resources at operation 130. UE may include at leastone of a list of destinations of communication, or QoS flow identifiers(IDs)/quality of service (QoS) profile IDs in sidelink UE informationmessage. The destination list can be separate for each type(broadcast/unicast/groupcast). Alternately UE may include communicationtype associated with each destination instead of separate list for eachcommunication type. gNB/BS configures V2X sidelink transmissionresources (mode 1, additionally mode 2 can also be configured) andtransmits information on the V2X sidelink transmission resources in anRRC reconfiguration message to the UE at operation 140. UE performs V2Xsidelink transmission using the configured resources at operation 150.

In an embodiment, Mode1 Supportedlnd may not be included in V2X SIB ifmode 2 transmission resource pool(s) are not included in V2X SIB.

In an embodiment, Mode1SupportedInd may not be included in V2X SIB. Ifthe V2X sidelink transmission requires mode 1 transmission resources, UEin RRC_IDLE/INACTIVE state initiates RRC connection.

FIG. 2 is another example illustration of a method according to anembodiment of the disclosure.

Referring to FIG. 2 , UE is in RRC_IDLE/INACTIVE state and interested inV2X sidelink transmission on frequency F1. UE acquires the V2X SIB(s)transmitted by the camped cell at operation 210. In this example, theacquired V2X SIB does not include mode 2 transmission resource pool(s)for frequency F1. Since the mode 2 transmission resource pool(s) forfrequency F1 are not included in V2X SIB, UE initiates an RRC connectionsetup/resume procedure at operation 220. After the RRC connection issetup at operation 220, UE transmits sidelink UE information message togNB/BS to indicate that it is interested in V2X sidelink transmission onfrequency F1 at operation 230. If the V2X sidelink transmission requiresmode 1 transmission resources, UE also indicates that it needs mode 1transmission resources at operation 230. UE may include at least one ofa list of destinations of communication, or QoS flow IDs/QoS profile IDsin sidelink UE information message. The destination list can be separatefor each type (broadcast/unicast/groupcast). Alternately UE may includecommunication type associated with each destination instead of separatelist for each communication type. In order to determine whether mode 1transmission resources are required for V2X sidelink transmission ornot, mapping between V2X services and mode1/mode 2 transmissionresources can be (pre-)configured. gNB/BS configures V2X sidelinktransmission resources (mode 1, additionally mode 2 can also beconfigured) and transmits information on the V2X sidelink transmissionresources in an RRC reconfiguration message to the UE at operation 240.UE performs V2X sidelink transmission using the configured resources atoperation 250.

FIG. 3 is another example illustration of a method according to anembodiment of the disclosure.

Referring to FIG. 3 , UE is in RRC_CONNECTED state and interested in V2Xsidelink transmission on frequency F1. UE acquires the V2X SIB(s)transmitted by the camped cell. UE transmits sidelink UE informationmessage to gNB/BS to indicate that it is interested in V2X sidelinktransmission on frequency F1 at operation 310. If the V2X sidelinktransmission requires mode 1 transmission resources, UE also indicatesthat it needs mode 1 transmission resources at operation 310. UE mayinclude at least one of a list of destinations of communication, or QoSflow IDs/QoS profile IDs in sidelink UE information message. Thedestination list can be separate for each type(broadcast/unicast/groupcast). Alternately UE may include communicationtype associated with each destination instead of separate list for eachcommunication type. In order to determine whether mode 1 transmissionresources are required for V2X sidelink transmission or not, mappingbetween V2X services and mode1/mode 2 transmission resources can be(pre-)configured. gNB/BS configures V2X sidelink transmission resources(mode 1, additionally mode 2 can also be configured) and transmitsinformation on the V2X sidelink transmission resources in an RRCreconfiguration message at operation 320. UE performs V2X sidelinktransmission using the configured resources at operation 330.

Connection Initiation Triggers for Congestion Control

In the RRC_IDLE/INACTIVE state, UE performs autonomous resourceselection. eNB provides TX resource pool(s). UE autonomously selects theresource(s) from the TX resource pool based on sensing. UE inRRC_IDLE/INACTIVE state may fail to obtain the resource in case ofcongestion or if channel busy ratio (CBR) is very high resulting intransmission failure. CBR is the portion of sub-channels whose S—RSSIexceed a (pre-)configured threshold.

FIG. 4 is an example illustration of a method according to an embodimentof the disclosure.

Referring to FIG. 4 , UE is in RRC_IDLE/INACTIVE state and interested inV2X sidelink transmission on frequency F1. UE acquires the V2X SIB(s)transmitted by the camped cell at operation 410. The acquired V2X SIBincludes mode 2 TX resource pool(s) for frequency F1. The V2X SIB alsoincludes information on duration for which the UE cannot selectresource, i.e. ResourceUnavailabilityDuration. The UE obtains the TXresource pool for V2X sidelink transmission from the V2X SIB. UEperforms sensing on V2X mode 2 TX resource pool to select the resourceat operation 420. UE shall initiate an RRC connection setup/resumeprocedure at operation 430, if it is not able to select resource (basedon sensing) for a (pre-)configured duration(ResourceUnavailabilityDuration). After the RRC connection is setup atoperation 430, UE transmits sidelink UE information message to gNB/BS toindicate that it is interested in V2X sidelink transmission on frequencyF1 at operation 440. UE can also include congestion indication in thesidelink UE information message, so that network can accordinglyconfigure mode 1 resources or mode 2 resource pool(s) and transmitinformation on mode 1 or 2 resources in an RRC reconfiguration messageto UE at operation 450.

FIG. 5 is an example illustration of a method according to an embodimentof the disclosure.

Referring to FIG. 5 , UE is in RRC_IDLE/INACTIVE state and interested inV2X sidelink transmission on frequency F1. UE acquires the V2X SIB(s)transmitted by the camped cell at operation 510. The acquired V2X SIBincludes mode 2 TX resource pool(s) for frequency F1. The V2X SIB alsoincludes information on CBR threshold for connection initiation, i.e.CBRThresholdforConnectionInitiation. The UE obtains the TX resource poolfor V2X sidelink transmission from the V2X SIB. UE performs sensing onTX resource pool to select the resource at operation 520. UE alsomeasures CBR on the TX resource pool at operation 530. The UE determineswhether CBR measured for TX resource pool is greater than(pre-)configured threshold, i.e. CBRThresholdforConnectionInitiation atoperation 535. UE shall initiate an RRC connection setup/resumeprocedure, if CBR measured for TX resource pool is greater than(pre-)configured threshold. In case there are multiple TX resourcepool(s), UE shall initiate an RRC connection setup/resume procedure, ifCBR measured for all TX resource pools is greater than (pre-)configuredthreshold. After the RRC connection is setup at operation 540, UEtransmits sidelink UE information message to gNB/BS to indicate that itis interested in V2X sidelink transmission on frequency F1 at operation550. UE can also include congestion indication in the sidelink UEinformation message, so that network can accordingly configure mode 1resources or mode 2 resource pool(s) to UE and transmit information onmode 1 or 2 resources in an RRC reconfiguration message to the UE atoperation 560.

NR Connection Initiation Triggers for V2X Sidelink Communication

There are two radio access technologies (RATs) for V2X sidelinkcommunication. LTE V2X sidelink communication supports broadcastcommunication and caters limited V2X use cases. NR V2X sidelinkcommunication supports unicast/broadcast/groupcast communication foradvanced V2X uses cases. V2X services are mapped to NR and/or LTEsidelink. GNB (or NR cell) can configure V2X sidelink communicationconfiguration for NR sidelink, or gNB (or NR cell) can configure V2Xsidelink communication configuration for LTE sidelink, or gNB (or NRcell) can configure V2X sidelink communication configuration for LTEsidelink and NR sidelink. NR V2X SI includes the following to supportthe above configurations:

-   -   1. NR V2X sidelink (SL) inter carrier frequency list        -   TX resource pool(s) for listed frequency is optionally            included    -   2. LTE V2X SL inter carrier frequency list        -   TX resource pool(s) for listed frequency is optionally            included    -   3. NR V2X SL configuration for serving frequency        -   TX resource pool(s) is optionally included    -   4. LTE V2X SL configuration for serving frequency        -   TX resource pool(s) is optionally included

Scenario 1: UE is camped on cell of first RAT (i.e. NR) but interestedin V2X sidelink communication based on second RAT (i.e. LTE) on thecamped frequency.

FIG. 6 illustrates a method for NR connection initiation triggers forV2X sidelink communication according to an embodiment of the disclosure.

In one method of this disclosure as illustrated in FIG. 6 , it isproposed that UE camped on an NR cell, initiates an RRC connection onthe NR cell, if the frequency on which the UE is configured to transmitLTE V2X sidelink communication concerns the camped frequency (i.e.frequency of NR cell); and if the system information (i.e. V2X SIB)received/acquired from the camped cell (i.e. NR cell) includes LTE V2Xsidelink communication configuration/parameters for the camped frequencybut does not include transmission resource pool for LTE V2X sidelinkcommunication on the camped frequency. In an embodiment, NR cell maytransmit LTE V2X sidelink communication configuration/parameters and NRV2X sidelink communication configuration/parameters in different V2XSIBs.

Referring to FIG. 6 , UE camped on an NR cell on frequency F1 is inRRC_IDLE/INACTIVE state and interested in LTE V2X sidelink transmissionon frequency F1. The UE receives V2X SIB(s) from the NR cell onfrequency F1 at operation 610. The V2X SIB(s) may include at least oneof NR V2X SL inter carrier frequency list, LTE V2X SL inter carrierfrequency list, NR V2X SL configuration for serving frequency, or LTEV2X SL configuration for serving frequency. In addition, the V2X SIB(s)may optionally include NR and/or LTE TX resource pool(s) for the listedfrequency or the serving frequency. The UE determines, if F1 is thecamped frequency, and if LTE V2X SL configuration is received in V2X SI,and if LTE V2X SL TX resource pool for F1 is received based on thereceived V2X SIB. It is assumed that in this case of FIG. 6 , the V2XSIB includes LTE V2X SL configuration for F1 but does not include LTEV2X SL TX resource pool for F1. In the case of FIG. 6 that F1 is thecamped frequency, and LTE V2X SL configuration is received in V2X SI,and LTE V2X SL TX resource pool for F1 is not received, the UE initiatesan NR RRC connection setup/resume procedure at operation 620. After theRRC connection is setup at operation 620, the UE transmits a sidelink UEinformation message to the NR cell (i.e. gNB) on frequency F1 toindicate that UE is interested in LTE V2X sidelink communicationtransmission or to request resources for LTE V2X SL communicationtransmission at operation 630. In an embodiment, different sidelink UEinformation messages (e.g. LTE sidelink UE information message and NRsidelink UE information message) can be used for LTE V2X SLcommunication and NR V2X SL communication. Based on the received message(LTE sidelink UE information message and NR sidelink UE informationmessage) gNB can identify whether UE is interested in LTE V2X sidelinkcommunication transmission or NR V2X sidelink communication transmissionand accordingly provide LTE V2X sidelink communication transmission orNR V2X sidelink communication transmission resources. Alternately, samesidelink UE information message can be used for the LTE V2X SLcommunication and the NR V2X SL communication wherein message includesseparate fields/information elements (IEs) for LTE V2X SL communicationand NR V2X SL communication and UE includes them accordingly.

The gNB configures LTE sidelink communication resources, and transmitsan RRC reconfiguration including information on the LTE sidelinkcommunication transmission resources to the UE at operation 640.

Scenario 2: UE is camped on cell of first RAT (i.e. NR) but interestedin sidelink communication based on second RAT (i.e. LTE) on frequencyother than the camped frequency.

FIG. 7 illustrates another method for NR connection initiation triggersfor V2X sidelink communication according to an embodiment of thedisclosure.

In one method of this disclosure as illustrated in FIG. 7 , it isproposed that UE camped on an NR cell, initiates an RRC connection on NRcell, if the frequency on which the UE is configured to transmit LTE V2Xsidelink communication is included in V2X inter frequency informationlist for LTE V2X sidelink communication broadcasted in systeminformation (i.e. V2X SIB) transmitted by NR cell; and if the systeminformation (i.e. V2X SIB) broadcasted by the camped cell does notinclude transmission resource pool for LTE V2X sidelink communication onthe concerned frequency. In an embodiment, NR cell may transmit LTE V2Xsidelink communication configuration/parameters and NR V2X sidelinkcommunication configuration/parameters in different V2X SIBs.

Referring to FIG. 7 , UE camped on an NR cell on frequency F1 is inRRC_IDLE/INACTIVE state and interested in LTE V2X sidelink transmissionon frequency F2. The UE receives V2X SIB(s) from the NR cell onfrequency F1 at operation 710. The V2X SIB(s) may include at least oneof NR V2X SL inter carrier frequency list, LTE V2X SL inter carrierfrequency list, NR V2X SL configuration for serving frequency, or LTEV2X SL configuration for serving frequency. In addition, the V2X SIB(s)may optionally include NR and/or LTE TX resource pool(s) for the listedfrequency or the serving frequency. The UE determines, if F2 is servingfrequency, and if F2 is included in LTE V2X SL frequency list, and ifLTE V2X SL TX resource pool for F2 is received based on the received V2XSIB. It is assumed that in this case of FIG. 7 , the V2X SIB includesLTE V2X SL inter carrier frequency list, and the LTE V2X SL intercarrier frequency list includes F2, but does not include LTE V2X SL TXresource pool for F2. In the case of FIG. 7 that F2 is not servingfrequency, and F2 is included in LTE V2X SL frequency list received inV2X SIB, and LTE V2X SL TX resource pool for F2 is not received, the UEinitiates an NR RRC connection setup/resume procedure at operation 720.After the RRC connection is setup at operation 720, the UE transmits asidelink UE information message to the NR cell (i.e. gNB) on frequencyF1 to indicate that UE is interested in LTE V2X sidelink communicationtransmission or to request resources for LTE V2X SL communicationtransmission at operation 730. The gNB configures LTE sidelinkcommunication transmission resources, and transmits an RRCreconfiguration including information on the LTE sidelink communicationtransmission resources to the UE at operation 740. In an embodiment,different sidelink UE information messages (e.g. LTE sidelink UEinformation message and NR sidelink UE information message) can be usedfor LTE V2X SL communication and NR V2X SL communication. Based on thereceived message (LTE sidelink UE information message and NR sidelink UEinformation message) gNB can identify whether UE is interested in LTEV2X sidelink communication transmission or NR V2X sidelink communicationtransmission and accordingly provide LTE V2X sidelink communicationtransmission or NR V2X sidelink communication transmission resources.Alternately, same sidelink UE information message can be used for theLTE V2X SL communication and the NR V2X SL communication wherein messageincludes separate fields/IEs for LTE V2X SL communication and NR V2X SLcommunication and UE includes them accordingly.

Scenario 3: UE is camped on cell of first RAT (i.e. NR) and interestedin sidelink communication based on first RAT (i.e. NR) on the campedfrequency.

FIG. 8 illustrates another method for NR connection initiation triggersfor V2X sidelink communication according to an embodiment of thedisclosure.

In one method of this disclosure as illustrated in FIG. 8 , it isproposed that UE camped on an NR cell, initiates an RRC connection onthe NR cell, if the frequency on which the UE is configured to transmitNR V2X sidelink communication concerns the camped frequency; and if thesystem information (i.e. V2X SIB) broadcasted by the camped cellincludes NR V2X sidelink communication configuration/parameters for thecamped frequency but does not include transmission resource pool for NRV2X sidelink communication on the camped frequency. In an embodiment, NRcell may transmit LTE V2X sidelink communicationconfiguration/parameters and NR V2X sidelink communicationconfiguration/parameters in different V2X SIBs.

Referring to FIG. 8 , UE camped on an NR cell on frequency F1 is inRRC_IDLE/INACTIVE state and interested in NR V2X sidelink transmissionon frequency F1. The UE receives V2X SIB(s) from the NR cell onfrequency F1 at operation 810. The V2X SIB may include at least one ofNR V2X SL inter carrier frequency list, LTE V2X SL inter carrierfrequency list, NR V2X SL configuration for serving frequency, or LTEV2X SL configuration for serving frequency. In addition, the V2X SIB mayoptionally include NR and/or LTE TX resource pool(s) for the listedfrequency or the serving frequency. The UE determines, if F1 is thecamped frequency, and if NR V2X SL configuration is received in V2X SI,and if NR V2X SL TX resource pool for F1 is received based on thereceived V2X SIB. It is assumed that in this case of FIG. 8 , the V2XSIB includes NR V2X SL configuration for F1 but does not include NR V2XSL TX resource pool for F1. In the case of FIG. 8 that F1 is the campedfrequency, and NR V2X SL configuration is received in V2X SI, and NR V2XSL TX resource pool for F1 is not received, the UE initiates an NR RRCconnection setup/resume procedure at operation 820. After the RRCconnection is setup at operation 820, the UE transmits a sidelink UEinformation message to the NR cell (i.e. gNB) on frequency F1 toindicate that UE is interested in NR V2X sidelink communicationtransmission or to request NR V2X SL communication transmissionresources at operation 830. The gNB configures NR sidelink communicationtransmission resources, and transmits an RRC reconfiguration includinginformation on the NR sidelink communication resources to the UE atoperation 840. In an embodiment, different sidelink UE informationmessages (e.g. LTE sidelink UE information message and NR sidelink UEinformation message) can be used for LTE V2X SL communication and NR V2XSL communication. Based on the received message (LTE sidelink UEinformation message and NR sidelink UE information message) gNB canidentify whether UE is interested in LTE V2X sidelink communicationtransmission or NR V2X sidelink communication transmission andaccordingly provide LTE V2X sidelink communication transmission or NRV2X sidelink communication transmission resources. Alternately, samesidelink UE information message can be used for the LTE V2X SLcommunication and the NR V2X SL communication wherein message includesseparate fields/IEs for LTE V2X SL communication and NR V2X SLcommunication and UE includes them accordingly.

Scenario 4: UE is camped on cell of first RAT (i.e. NR) and interestedin sidelink communication based on first RAT (i.e. NR) on frequencyother than the camped frequency.

FIG. 9 illustrates another method for NR connection initiation triggersfor V2X sidelink communication according to an embodiment of thedisclosure.

In one method of this disclosure as illustrated in FIG. 9 , it isproposed that UE camped on an NR cell, initiates an RRC connection on NRcell, if the frequency on which the UE is configured to transmit NR V2Xsidelink communication is included in V2X inter frequency informationlist for NR sidelink communication broadcasted in system information(i.e. V2X SIB) transmitted by NR cell; and if the system information(i.e. V2X SIB) broadcasted by the camped cell does not includetransmission resource pool for NR V2X sidelink communication on theconcerned frequency. In an embodiment, NR cell may transmit LTE V2Xsidelink communication configuration/parameters and NR V2X sidelinkcommunication configuration/parameters in different V2X SIBs.

Referring to FIG. 9 , UE camped on an NR cell on frequency F1 is inRRC_IDLE/INACTIVE state and interested in NR V2X sidelink transmissionon frequency F2. The UE receives V2X SIB(s) from the NR cell onfrequency F1 at operation 910. The V2X SIB may include at least one ofNR V2X SL inter carrier frequency list, LTE V2X SL inter carrierfrequency list, NR V2X SL configuration for serving frequency, or LTEV2X SL configuration for serving frequency. In addition, the V2X SIB mayoptionally include NR and/or LTE TX resource pool(s) for the listedfrequency or the serving frequency. The UE determines, if F2 is servingfrequency, and if F2 is included in NR V2X SL frequency list, and if NRV2X SL TX resource pool for F2 is received based on the received V2XSIB. It is assumed that in this case of FIG. 9 , the V2X SIB includes NRV2X SL inter carrier frequency list, and the NR V2X SL inter carrierfrequency list includes F2, but does not include NR V2X SL TX resourcepool for F2. In the case of FIG. 9 that F2 is not serving frequency, andF2 is included in NR V2X SL frequency list received in V2X SIB, and NRV2X SL TX resource pool for F2 is not received, the UE initiates an NRRRC connection setup procedure at operation 920. After the RRCconnection is setup at operation 920, the UE transmits a sidelink UEinformation message to the NR cell (i.e. gNB) on frequency F1 toindicate that UE is interested in NR V2X sidelink communicationtransmission or to request resources for NR V2X SL communicationtransmission at operation 930. The gNB configures NR V2X sidelinkcommunication transmission resources, and transmits an RRCreconfiguration including information on the NR sidelink communicationtransmission resources to the UE at operation 940. In an embodiment,different sidelink UE information messages (e.g. LTE sidelink UEinformation message and NR sidelink UE information message) can be usedfor LTE V2X SL communication and NR V2X SL communication. Based on thereceived message (LTE sidelink UE information message and NR sidelink UEinformation message) gNB can identify whether UE is interested in LTEV2X sidelink communication transmission or NR V2X sidelink communicationtransmission and accordingly provide LTE V2X sidelink communicationtransmission or NR V2X sidelink communication transmission resources.Alternately, same sidelink UE information message can be used for theLTE V2X SL communication and the NR V2X SL communication wherein messageincludes separate fields/IEs for LTE V2X SL communication and NR V2X SLcommunication and UE includes them accordingly.

LTE Connection Initiation Triggers for V2X Sidelink Communication

There are two RATs for V2X sidelink communication. LTE V2X sidelinkcommunication supports broadcast communication and caters limited V2Xuse cases. NR V2X sidelink communication supportsunicast/broadcast/groupcast communication for advanced V2X uses cases.V2X services are mapped to NR and/or LTE sidelink. ENB (or LTE cell) canconfigure V2X sidelink communication configuration for NR sidelink, oreNB (or LTE cell) can configure V2X sidelink communication configurationfor LTE sidelink, or eNB (or LTE cell) can configure V2X sidelinkcommunication configuration for LTE sidelink and NR sidelink. LTE V2X SIincludes the following to support the above configurations:

-   -   1. NR V2X SL inter carrier frequency list        -   TX resource pool(s) for listed frequency is optionally            included    -   2. LTE V2X SL inter carrier frequency list        -   TX resource pool(s) for listed frequency is optionally            included    -   3. NR V2X SL configuration for serving frequency        -   TX resource pool(s) is optionally included    -   4. LTE V2X SL configuration for serving frequency        -   TX resource pool(s) is optionally included

Scenario 1: UE is camped on cell of second RAT (i.e. LTE) but interestedin sidelink communication based on first RAT (i.e. NR) on the campedfrequency.

FIG. 10 illustrates a method for LTE connection initiation triggers forV2X sidelink communication according to an embodiment of the disclosure.

In one method of this disclosure as illustrated in FIG. 10 , it isproposed that UE camped on an LTE cell, initiates an RRC connection onthe LTE cell, if the frequency on which the UE is configured to transmitNR V2X sidelink communication concerns the camped frequency; and if thesystem information (i.e. V2X SIB) broadcasted by the camped cellincludes NR V2X sidelink communication configuration for the campedfrequency (i.e. frequency of LTE cell) but does not include transmissionresource pool for NR V2X sidelink communication on the camped frequency.

Referring to FIG. 10 , UE camped on an LTE cell on frequency F1 is inRRC_IDLE/INACTIVE state and interested in NR V2X sidelink transmissionon frequency F1. The UE receives V2X SIB(s) from the LTE cell onfrequency F1 at operation 1010. The V2X SIB(s) may include at least oneof NR V2X SL inter carrier frequency list, LTE V2X SL inter carrierfrequency list, NR V2X SL configuration for serving frequency, or LTEV2X SL configuration for serving frequency. In addition, the V2X SIB(s)may optionally include NR and/or LTE TX resource pool(s) for the listedfrequency or the serving frequency. The UE determines, if F1 is thecamped frequency, and if NR V2X SL configuration is received in V2X SIB,and if NR V2X SL TX resource pool for F1 is received based on thereceived V2X SIB. It is assumed that in this case of FIG. 10 , the V2XSIB includes NR V2X SL configuration for F1 but does not include NR V2XSL TX resource pool for F1. In the case of FIG. 10 that F1 is the campedfrequency, and NR V2X SL configuration is received in V2X SI, and NR V2XSL TX resource pool for F1 is not received, the UE initiates an LTE RRCconnection setup/resume procedure at operation 1020. After the RRCconnection is setup at operation 1020, the UE transmits a sidelink UEinformation message to the LTE cell (i.e. eNB) on frequency F1 toindicate that UE is interested in NR V2X sidelink communicationtransmission or to request NR V2X SL communication transmission atoperation 1030. The eNB configures NR sidelink communicationtransmission resources, and transmits an RRC reconfiguration includinginformation on the NR sidelink communication resources to the UE atoperation 1040. It is to be noted different sidelink UE informationmessages (e.g. LTE sidelink UE information message and NR sidelink UEinformation message) can be used for LTE V2X SL communication and NR V2XSL communication. Alternately, same sidelink UE information message canbe used for the LTE V2X SL communication and the NR V2X SL communicationwherein message includes separate fields/IEs for LTE V2X SLcommunication and NR V2X SL communication and UE includes themaccordingly.

Scenario 2: UE is camped on cell of second RAT (i.e. LTE) but interestedin sidelink communication based on first RAT (i.e. NR) on frequencyother than the camped frequency.

FIG. 11 illustrates another method for LTE connection initiationtriggers for V2X sidelink communication according to an embodiment ofthe disclosure.

In one method of this disclosure as illustrated in FIG. 11 , it isproposed that UE camped on an LTE cell, initiates an RRC connection onLTE cell, if the frequency on which the UE is configured to transmit NRV2X sidelink communication is included in V2X inter frequencyinformation list for NR sidelink communication broadcasted in systeminformation (i.e. V2X SIB) transmitted by LTE cell; and if the systeminformation (i.e. V2X SIB) broadcasted by the camped cell does notinclude transmission resource pool for NR V2X sidelink communication onthe concerned frequency.

Referring to FIG. 11 , UE camped on an LTE cell on frequency F1 is inRRC_IDLE/INACTIVE state and interested in NR V2X sidelink transmissionon frequency F2. The UE receives V2X SIB(s) from the LTE cell onfrequency F1 at operation 1110. The V2X SIB may include at least one ofNR V2X SL inter carrier frequency list, LTE V2X SL inter carrierfrequency list, NR V2X SL configuration for serving frequency, or LTEV2X SL configuration for serving frequency. In addition, the V2X SIB mayoptionally include NR and/or LTE TX resource pool(s) for the listedfrequency or the serving frequency. The UE determines, if F2 is servingfrequency, and if F2 is included in NR V2X SL frequency list, and if NRV2X SL TX resource pool for F2 is received based on the received V2XSIB. It is assumed that in this case of FIG. 11 , the V2X SIB includesNR V2X SL inter carrier frequency list, and the NR V2X SL inter carrierfrequency list includes F2, but does not include NR V2X SL TX resourcepool for F2. In the case of FIG. 11 that F2 is not serving frequency,and F2 is included in NR V2X SL frequency list received in V2X SIB, andNR V2X SL TX resource pool for F2 is not received, the UE initiates anLTE RRC connection setup/resume procedure at operation 1120. After theRRC connection is setup at operation 1120, the UE transmits a sidelinkUE information message to the LTE cell (i.e. eNB) on frequency F1 toindicate that UE is interested in NR V2X sidelink communicationtransmission or to request NR V2X SL communication transmission atoperation 1130. The eNB configures NR sidelink communicationtransmission resources, and transmits an RRC reconfiguration includinginformation on the NR sidelink communication transmission resources tothe UE at operation 1140. It is to be noted different sidelink UEinformation messages (e.g. LTE sidelink UE information message and NRsidelink UE information message) can be used for LTE V2X SLcommunication and NR V2X SL communication. Alternately, same sidelink UEinformation message can be used for the LTE V2X SL communication and theNR V2X SL communication wherein message includes separate fields/IEs forLTE V2X SL communication and NR V2X SL communication and UE includesthem accordingly.

Scenario 3: UE is camped on cell of second RAT (i.e. LTE) and interestedin sidelink communication based on second RAT (i.e. LTE) on the campedfrequency.

In one method of this disclosure, it is proposed that UE camped on anLTE cell, initiates an RRC connection on the LTE cell, if the frequencyon which the UE is configured to transmit LTE V2X sidelink communicationconcerns the camped frequency; and if the system information (i.e. V2XSIB) broadcasted by the camped cell includes LTE V2X sidelinkconfiguration for the camped frequency but does not include transmissionresource pool for LTE V2X sidelink communication on the campedfrequency.

Scenario 4: UE is camped on cell of second RAT (i.e. LTE) and interestedin sidelink communication based on second RAT (i.e. LTE) on frequencyother than the camped frequency.

In one method of this disclosure, it is proposed that UE camped on anLTE cell, initiates an RRC connection on the LTE cell, if the frequencyon which the UE is configured to transmit LTE V2X sidelink communicationis included in V2X inter frequency information list for LTE sidelinkcommunication broadcasted in system information (i.e. V2X SIB)transmitted by LTE cell; and if the system information (i.e. V2X SIB)broadcasted by the camped cell does not include transmission resourcepool for LTE V2X sidelink communication on the concerned frequency.

In NR, bandwidth part (BWP) is defined for SL, and the same SL BWP isused for sidelink transmission and reception. In a licensed carrier, SLBWP is defined separately from Uu BWP. One SL BWP is (pre-)configuredfor RRC_IDLE and out-of-coverage NR V2X UEs in a carrier. For UEs inRRC_CONNECTED mode, one SL BWP is active in a carrier. No signaling isexchanged over SL for the activation or deactivation of a SL BWP. Onlyone SL BWP is configured in a carrier.

FIG. 12 shows SL BWP and UL BWP depending on the configuration accordingto an embodiment of the disclosure.

Referring to FIG. 12 , depending on the configuration, SL BWP and UL BWPcan be a) non overlapping, b) fully overlapping or c) partialoverlapping.

In LTE sidelink operation, when the UL transmission overlaps in timedomain with V2X sidelink transmission in the same frequency (carrier),the UE prioritizes the V2X sidelink transmission over the ULtransmission if the proximity services (ProSe) per packet priority(PPPP) of sidelink media access control (MAC) protocol data unit (PDU)is lower than a (pre)configured PPPP threshold; otherwise, the UEprioritizes the UL transmission over the V2X sidelink transmission.

In NR, in case of non-overlapping active SL BWP and active UL BWP evenif the UL transmission overlaps in time domain with V2X sidelinktransmission, depending on the UE capability, UE may or may not be ableto transmit simultaneously on SL BWP and UL BWP on a carrier. If the UEcan transmit simultaneously on SL BWP and UL BWP and sidelink MAC PDUmeets certain criteria (e.g. priority is lower than a threshold, lowvalue means high priority), it can reduce UL transmission power. If theUE cannot transmit simultaneously on SL BWP and UL BWP and sidelink MACPDU meets certain criteria (e.g. priority value is lower than athreshold, low value means high priority), it can prioritize the V2Xsidelink transmission over the UL transmission.

In case of overlapped active SL and UL BWPs on a carrier, UE cannottransmit both SL and UL transmission simultaneously. So, UE shouldprioritize between SL and UL transmission. UE prioritizes the V2Xsidelink transmission over the UL transmission if sidelink MAC PDU meetscertain criteria (e.g. priority is lower than a threshold, low valuemeans high priority).

In an embodiment, if both mode 1 and mode 2 transmission resources areconfigured to UE, network can indicate for which traffic UE uses whichtransmission resource. Network can indicate communication typeassociated with each type (mode1/mode2) of transmission resources. Forexample, network can indicate that mode 1 transmission resources are tobe used for unicast communication, whereas mode 2 transmission resourcesare to be used for broadcast/groupcast. So, UE will use the configuredmode 1 and mode 2 resources accordingly.

Alternately, network can indicate QoS profiles/QoS flow IDs associatedwith each type (mode1/mode2) of transmission resources. For example,network can indicate that mode 1 transmission resources are to be usedfor QoS flows X/Y, whereas mode 2 transmission resources are for others.So, UE will use the configured mode 1 and mode 2 resources accordingly.

Alternately, network can indicate logical channels (LCHs) or logicalchannel groups (LCGs) associated with each type (mode1/mode2) oftransmission resources. For example, network can indicate that mode 1transmission resources are to be used for LCHs or LCGs X/Y, whereas mode2 transmission resources are for others. So, UE will use the configuredmode 1 and mode 2 resources accordingly.

Alternately, network can indicate priority associated with each type(mode1/mode2) of transmission resources. For example, network canindicate that mode 1 transmission resources are to be used forpriorities X/Y, whereas mode 2 transmission resources are for others.So, UE will use the configured mode 1 and mode 2 resources accordingly.

Alternately, network can indicate priority threshold. For example,network can indicate that mode 1 transmission resources are to be usedfor logical channels with priorities lower than the priority threshold,whereas mode 2 transmission resources are for others. So, UE will usethe configured mode 1 and mode 2 resources accordingly.

Source Layer 2 ID Transmission Mechanism

FIG. 13 shows an LTE sidelink MAC PDU format according to an embodimentof the disclosure.

Referring to FIG. 13 , in LTE sidelink MAC PDU format, source layer-2 IDis always included in SL-shared channel (SCH) sub-header of every MACPDU transmitted by V2X TX UE on sidelink. Source layer-2 ID is 24 bitsand access stratum in UE receives source layer 2 ID from higher layer.Destination layer-2 ID is also included in SL-SCH sub-header of everyMAC PDU transmitted by V2X TX UE on sidelink. Destination layer-2 ID is24 bits and access stratum in UE receives destination layer 2 ID fromhigher layer.

Physical sidelink common control channel (PSCCH) and physical sidelinkshared channel (PSSCH) are used for data TX/reception (RX). Sidelinkcontrol information (SCI) is transmitted on PSCCH. Transport block(includes MAC PDU) is transmitted on PSSCH.

LTE sidelink only supports broadcast communication for V2X sidelinkcommunication. Hybrid automatic repeat request (HARQ) feedback is notsupported and UE autonomously performs fixed number of retransmissions.NR V2X Sidelink communication supports unicast/groupcast/broadcastcommunication. NR V2X supports HARQ feedback for unicast/groupcast. HARQfeedback can be enabled/disabled. Considering the above characteristicsof NR V2X communication, it is not efficient to always include sourcelayer-2 ID in SL SCH MAC header. A method to determine whether toinclude source layer-2 ID in SL SCH MAC header or not is needed.

Method 1

FIG. 14 illustrates a source layer 2 transmission mechanism according toan embodiment of the disclosure.

In one method of the disclosure as illustrated in FIG. 14 , it isproposed that TX UE includes source layer 2 ID in MAC PDU and/or PSCCHbased on communication type (broadcast or groupcast or unicast)associated with transmission and whether HARQ feedback is enabled or notfor that communication type.

Referring to FIG. 14 , TX UE determines the communication typeassociated with MAC PDU at operation 1410. If the MAC PDU corresponds tobroadcast communication, the TX UE includes full source layer-2 ID in SLMAC header at operation 1420. The MAC PDU corresponds to broadcastcommunication if it includes MAC service data unit(s) (SDU(s)) of SLresource block(s) (RB(s))/LCHs associated with broadcast communication.

Else if MAC PDU corresponds to unicast communication, the TX UEdetermines whether HARQ feedback is enabled at operation 1430. If HARQfeedback is enabled for unicast communication, the TX UE partitionssource layer-2 ID in two parts. The TX UE includes first part of sourcelayer-2 ID in SL MAC header at operation 1440. The TX UE includes secondpart of source layer-2 ID in PSCCH at operation 1450. Second part ofsource layer-2 ID can be used to mask cyclic redundancy check (CRC) ofPSCCH, or second part of source layer-2 ID can be included in SCI ofPSCCH, or second part of source layer-2 ID can be further divided in twoparts. One part is used to mask CRC of PSCCH and other part is includedin SCI of PSCCH. In an embodiment, first part can be ‘X’ LSBs of sourcelayer-2 ID and second part includes the remaining bits of source layer-2ID. Else, i.e. if the HARQ feedback is disabled for unicastcommunication, the TX UE includes full source layer-2 ID in SL MACheader at operation 1460. MAC PDU corresponds to unicast communicationif it includes MAC SDU(s) of SL RB(s)/LCHs associated with broadcastunicast communication.

Else if MAC PDU corresponds to groupcast communication, the TX UEdetermines whether HARQ feedback is enabled at operation 1430. If HARQfeedback is enabled for groupcast communication, the TX UE partitionssource layer-2 ID in two parts. The TX UE includes first part of sourcelayer-2 ID in SL MAC header at operation 1440. The TX UE includes secondpart of source layer-2 ID in PSCCH at operation 1450. Second part ofsource layer-2 ID can be used to mask CRC of PSCCH, or second part ofsource layer-2 ID can be included in SCI of PSCCH, or second part ofsource layer-2 ID can be further divided in two parts. One part is usedto mask CRC of PSCCH and other part is included in SCI of PSCCH. In anembodiment, first part can be ‘X’ LSBs of source layer-2 ID and secondpart includes the remaining bits of source layer-2 ID. Else, i.e. if theHARQ feedback is disabled for groupcast communication, the TX UEincludes full source layer-2 ID in SL MAC header at operation 1460. MACPDU corresponds to groupcast communication if it includes MAC SDU(s) ofSL RB(s)/LCHs associated with groupcast communication.

Whether HARQ feedback is enabled for unicast communication or not can beconfigured by gNB via system information or dedicated RRC signaling.Alternately, it can be pre-configured.

Whether HARQ feedback is enabled for groupcast communication or not canbe configured by gNB via system information or dedicated RRC signaling.Alternately, it can be pre-configured.

In this method, depending on communication type (broadcast or groupcastor unicast) associated with transmission and whether HARQ feedback isenabled or not for that communication type, either full source layer-2ID is included in MAC PDU or partial of source layer-2 ID as summarizedin Table 1 below.

TABLE 1 Source Layer-2 ID In Communication Type SL SCH MAC HeaderBroadcast (no HARQ feedback) Full Source Layer-2 ID Unicast withfeedback 1st Part of Source Layer-2 ID in MAC header 2nd Part of SourceLayer-2 ID in PSCCH Unicast without feedback Full Source Layer-2 IDGroupcast with feedback 1st Part of Source Layer-2 ID in MAC header 2ndPart of Source Layer-2 ID in PSCCH Groupcast without feedback FullSource Layer-2 ID

In order to enable receiver to determine whether MAC header includesfull source layer-2 ID or partial source layer-2 ID following approachesare proposed:

-   -   1) One bit (or version number) in MAC header can indicate        whether header includes full or part of source layer-2 ID.    -   2) One bit in SCI (PSCCH) can indicate whether SCI includes part        of source layer-2 ID or not. Bit=1 indicates that SCI includes        part of source layer-2 ID; and that MAC header includes other        part. Bit=0 indicates that SCI does not include part of source        layer-2 ID; and that MAC header includes full source layer-2 ID.        Instead of including in SCI, this bit can be included in CRC        mask.    -   3) One bit HARQ feedback type can be included in SCI (PSCCH).        Bit=0 refers to no HARQ feedback, and indicates that MAC header        includes full source layer-2 ID; and that SCI does not include        part of source layer-2 ID. Bit=1 refers to HARQ feedback, and        indicates that SCI includes part of source layer-2 ID; and that        MAC header includes other part. Instead of including in SCI,        this bit can be included in CRC mask.    -   4) SCI format X can be for case of HARQ feedback or for case        where part of source layer-2 ID is included in SCI. SCI format Y        can be used for other case (i.e. no HARQ feedback or MAC header        includes full source layer-2 ID; SCI does not include part of        source layer-2 ID).    -   5) Communication type (unicast, broadcast, groupcast) and HARQ        feedback type (feedback or no feedback) can be included in PSCCH        (in SCI and/or CRC).

Method 2

FIG. 15 illustrates another source layer 2 transmission mechanismaccording to an embodiment of the disclosure.

In one method of the disclosure as illustrated in FIG. 15 , it isproposed that TX UE includes source layer-2 ID in MAC PDU and/or PSCCHbased on communication type (broadcast or groupcast or unicast)associated with transmission and whether HARQ feedback is enabled or notfor that communication type.

Referring to FIG. 15 , TX UE determines the communication typeassociated with MAC PDU at operation 1510. If MAC PDU corresponds tobroadcast communication, the TX UE includes full source layer-2 ID in SLMAC header at operation 1520. The MAC PDU corresponds to broadcastcommunication if it includes MAC SDU(s) of SL RB(s)/LCHs associated withbroadcast communication.

Else if MAC PDU corresponds to unicast communication, the TX UEdetermines whether HARQ feedback is enabled at operation 1530. If HARQfeedback is enabled for unicast communication, the TX UE does notinclude source layer-2 ID in SL MAC header, and includes full sourcelayer-2 ID in PSCCH at operation 1540. Else, i.e. if HARQ feedback isdisabled for unicast communication, the TX UE includes full sourcelayer-2 ID in SL MAC header at operation 1550. MAC PDU corresponds tounicast communication if it includes MAC SDU(s) of SL RB(s)/LCHsassociated with unicast communication.

Else if MAC PDU corresponds to groupcast communication, the TX UEdetermines whether HARQ feedback is enabled at operation 1530. If HARQfeedback is enabled for groupcast communication, the TX UE does notinclude source layer-2 ID in SL MAC header, and includes full sourcelayer-2 ID in PSCCH at operation 1540. Else, i.e. if HARQ feedback isdisabled for groupcast communication, the TX UE includes full sourcelayer-2 ID in SL MAC header at operation 1550. MAC PDU corresponds tounicast communication if it includes MAC SDU(s) of SL RB(s)/LCHsassociated with groupcast communication.

In this method, depending on communication type (broadcast or groupcastor unicast) associated with transmission and whether HARQ feedback isenabled or not for that communication type, either full source layer-2ID is included in MAC PDU or in PSCCH as summarized in Table 2 below.

TABLE 2 Source Layer-2 ID In SL Communication Type SCH MAC HeaderBroadcast (no feedback) Full Source Layer-2 ID in MAC Header Unicastwith feedback Not present in MAC Header Full Source Layer-2 ID in PSCCHUnicast without feedback Full Source Layer-2 ID in MAC Header Groupcastwith feedback Not present in MAC Header Full Source Layer-2 ID in PSCCHGroupcast without feedback Full Source Layer-2 ID in MAC Header

In order to enable receiver to determine whether MAC header includesfull source layer-2 ID or not following approaches are proposed:

-   -   1) One bit in MAC header can indicate whether MAC header        includes full source layer-2 ID or not.    -   2) One bit in SCI (PSCCH) can indicate whether SCI includes full        source layer-2 ID or not. Bit=1 indicates that SCI includes full        source layer-2 ID; and that MAC header includes other part.        Bit=0 indicates that SCI does not include source layer-2 ID; and        that MAC header includes full source layer-2 ID. This bit can be        included in CRC mask of PSCCH instead of SCI.    -   3) One bit HARQ feedback type can be included in SCI (PSCCH).        Bit=0 refers to no HARQ feedback, and indicates that MAC header        includes full source layer-2 ID; and that SCI does not include        source layer-2 ID. Bit=1 refers to HARQ feedback, and indicates        that SCI includes full source layer-2 ID; and that MAC header        does not include source layer-2 ID. This bit can be included in        CRC mask of PSCCH instead of SCI.    -   4) SCI format X can be for case of HARQ feedback or for case        where source layer-2 ID is included in SCI. SCI format Y can be        used for other case (i.e. no HARQ feedback or MAC header        includes full source layer-2 ID; SCI does not include source        layer-2 ID).    -   5) Communication type (unicast, broadcast, groupcast) and HARQ        feedback type (feedback or no feedback) can be included in PSCCH        (in SCI and/or CRC).

Whether HARQ feedback is enabled for unicast communication or not can beconfigured by gNB via system information or dedicated RRC signaling.Alternately, it can be pre-configured.

Whether HARQ feedback is enabled for groupcast communication or not canbe configured by gNB via system information or dedicated RRC signaling.Alternately, it can be pre-configured.

Method 3

FIG. 16 illustrates another source layer 2 transmission mechanismaccording to an embodiment of the disclosure.

In one method of the disclosure as illustrated in FIG. 16 , it isproposed that TX UE includes source layer-2 ID in MAC PDU and/or PSCCHbased on communication type (broadcast or groupcast or unicast)associated with transmission.

Referring to FIG. 16 , TX UE determines the communication typeassociated with MAC PDU at operation 1610. If MAC PDU corresponds tobroadcast communication, the TX UE includes full source layer-2 ID in SLMAC header at operation 1620. The MAC PDU corresponds to broadcastcommunication if it includes MAC SDU(s) of SL RB(s)/LCHs associated withbroadcast communication.

Else if MAC PDU corresponds to unicast or groupcast communication, theTX UE partitions source layer-2 ID in two parts. The TX UE includesfirst part of source layer-2 ID in SL MAC header at operation 1630. TheTX UE includes second part of source layer-2 ID in PSCCH at operation1640. Second part of source layer-2 ID can be used to mask CRC of PSCCH,or second part of source layer-2 ID can be included in SCI of PSCCH, orsecond part of source layer-2 ID can be further divided in two parts.One part is used to mask CRC of PSCCH and other part is included in SCIof PSCCH. In an embodiment, first part can be ‘X’ LSBs of source layer-2ID and second part includes the remaining bits of source layer-2 ID. MACPDU corresponds to unicast or groupcast communication if it includes MACSDU(s) of SL RB(s)/LCHs associated with unicast or groupcastcommunication respectively.

In this method, depending on communication type (broadcast or groupcastor unicast) associated with transmission, either full or partial sourcelayer-2 ID is included in MAC PDU as summarized in Table 3 below.

TABLE 3 Source Layer-2 ID in SL Communication Type SCH MAC HeaderBroadcast Full Source Layer-2 ID in MAC header Unicast 1st Part ofSource Layer-2 ID in MAC header 2nd Part of Source Layer-2 ID in PSCCHGroupcast 1st Part of Source Layer-2 ID in MAC header 2nd Part of SourceLayer-2 ID in PSCCH

In order to enable receiver to determine whether MAC header includesfull source layer-2 ID or partial source layer-2 ID following approachesare proposed:

-   -   1) One bit in MAC header can indicate whether header includes        full or part of source layer-2 ID.    -   2) One bit in SCI (PSCCH) can indicate whether SCI includes part        of source Layer-2 ID or not. Bit=1 indicates that SCI includes        part of source layer-2 ID; and that MAC header includes other        part. Bit=0 indicates that SCI does not include part of source        layer-2 ID; and that MAC header includes full source layer-2 ID.        This bit can be included in CRC mask of PSCCH instead of SCI.    -   3) SCI format X can be for case where part of source layer-2 ID        is included in SCI. SCI format Y can be used for other case        (i.e. MAC header includes full Source Layer-2 ID; SCI does not        include source layer-2 ID).    -   4) Communication type (unicast, broadcast, groupcast) can be        included in PSCCH (in SCI and/or CRC).

Method 4

In one method of the disclosure, it is proposed that TX UE includessource layer-2 ID in MAC PDU and/or PSCCH based on communication type(broadcast or groupcast or unicast) associated with transmission.

If MAC PDU corresponds to broadcast communication, the TX UE includesfull source layer-2 ID in SL MAC header.

Else if MAC PDU corresponds to unicast or groupcast communication, theTX UE does not include source layer-2 ID in SL MAC header. The TX UEincludes full source layer-2 ID in PSCCH.

In this method, depending on communication type (broadcast or groupcastor unicast) source layer-2 ID is included or not included in MAC PDU assummarized in Table 4 below.

TABLE 4 Communication Type Source Layer-2 ID in SL SCH MAC HeaderBroadcast Full Source Layer-2 ID in MAC header Unicast Not present inMAC Header Full Source Layer-2 ID in PSCCH Groupcast Not present in MACHeader Full Source Layer-2 ID in PSCCH

In order to enable receiver to determine whether MAC header includesfull source layer-2 ID or partial source layer-2 ID following approachesare proposed:

-   -   1) One bit in MAC header can indicate whether header includes        full source layer-2 ID or not.    -   2) One bit in SCI (PSCCH) can indicate whether SCI includes full        source layer-2 ID or not. Bit=1 indicates that SCI includes        source layer-2 ID; and that MAC header does not include source        layer-2 ID. Bit=0 indicates that SCI does not include source        layer-2 ID; and that MAC header includes full source layer-2 ID.        This bit can be included in CRC mask of PSCCH instead of SCI.    -   3) SCI format X can be for case where source layer-2 ID is        included in SCI. SCI format Y can be used for other case (i.e.        MAC header includes full source layer-2 ID; SCI does not include        source layer-2 ID).    -   4) Communication type (unicast, broadcast, groupcast) can be        included in PSCCH (in SCI and/or CRC).

In one method, irrespective of whether MAC PDU corresponds to unicast orgroupcast or broadcast communication, the TX UE does not include sourcelayer-2 ID in SL MAC header. The TX UE includes full source layer-2 IDin PSCCH.

Resources for HARQ Retransmissions

In NR V2X sidelink communication, HARQ feedback is supported for unicastand groupcast communication.

Scenario: Transmitter, i.e. TX UE is in coverage and gNB configures mode1 resource for transmission.

Basic Operation: UE transmits SL buffer status report (BSR) to gNB. TXUE receives physical downlink control channel (PDCCH) addressed to SLV2X radio network temporary identifier (SL-V-RNTI) from gNB whereindownlink control information (DCI) indicates resource for SLtransmission. UE generates the MAC PDU. UE transmits PSCCH. UE transmitsSL transport block (TB) (incl. MAC PDU) on PSSCH. RX UE sends SL HARQfeedback (HARQ-acknowledge (ACK) or HARQ-negative ACK(NACK)) on physicalSL feedback channel (PSFCH).

Issue: In case TX UE receives sidelink HARQ-NACK from RX UE, the issueis how to perform HARQ retransmission, e.g. how the TX UE obtainsresource for HARQ retransmission.

Method 1: In one method of the disclosure, it is proposed that gNBconfigures scheduling request (SR) resource(s) for requesting SL grantfor HARQ retransmission. In case multiple SR configurations are signaledfor SL, gNB can indicate which of these SR configuration(s) are used forrequesting SL grant for HARQ retransmission. Upon receiving sidelinkHARQ-NACK from RX UE, UE transmits SR in SR resource configured forrequesting SL grant for HARQ retransmission. Upon receiving SR, gNBtransmits PDCCH indicating SL grant for HARQ retransmission.

FIG. 17 illustrates the timeline of an operation for requesting SL grantfor retransmission and FIG. 18 is a corresponding signaling flow betweentransmitter UE, receiver UE and gNB according to an embodiment of thedisclosure.

Referring to FIG. 18 , gNB transmits an RRC reconfiguration message toTX UE at operation 1810. The RRC reconfiguration message includes SRconfiguration for requesting HARQ retransmission resource, e.g.information on SR resources for retransmission. The gNB transmits an SLgrant on PDCCH at operation 1820. The TX UE transmits controlinformation on PSCCH and SL TB on PSSCH to RX UE based on the SL grantat operation 1830. If the RX UE fails to receive the SL TB from the TXUE, the RX UE transmits SL HARQ-NACK to the TX UE at operation 1840. Ifthe TX UE receives HARQ-NACK from the RX UE, the TX UE transmits SR forHARQ retransmission resource to the gNB based on the SR configuration atoperation 1850. The gNB transmits an SL grant on PDCCH at operation1860. The TX UE transmits control information on PSCCH and SL TB onPSSCH to the RX UE based on the SL grant at operation 1870. If the RX UEreceives the SL TB from the TX UE, the RX UE transmits SL HARQ-ACK tothe TX UE at operation 1880.

If gNB allocates multiple SL grants one after another, on receiving SR,gNB may not be able to identify for which SL grant UE is requesting forretransmission.

FIG. 19 illustrates the timeline of an operation for requesting SL grantfor retransmission according to an embodiment of the disclosure.

Referring to FIG. 19 , gNB has allocated two SL grants, and TX UE hastransmitted two transport blocks to receiver UE based on these SLgrants. TX UE receives HARQ-ACK for transmission based on SL grant 1 andreceives HARQ-NACK for transmission based on SL grant 2. Upon receivingsidelink HARQ-NACK from RX UE, UE transmits SR in SR resource configuredfor requesting SL grant for HARQ retransmission. However, upon receivingSR, gNB cannot identify whether the SR is for HARQ retransmissionresource request for SL grant 1 or SL grant 2.

To overcome the above issue, it is proposed in this disclosure toinclude grant index in DCI allocating SL grant as illustrated in thetimeline of FIG. 20 . In particular, referring to FIG. 20 , SRconfiguration(s) to be used for requesting SL grant for HARQretransmission are linked to grant index. gNB indicates which SRconfiguration(s) is for which grant index(s). Upon receiving sidelinkHARQ-NACK for HARQ transmission corresponding to a SL grant with grantindex x, UE transmits SR in SR resource of SR configurationcorresponding to the grant index x.

HARQ-NACK is received for transmission corresponding to grant index 2,so UE transmits SR using SR resource of SR configuration linked to grantindex 2. The earliest available SR resource from SR configuration likedto grant index 2 is used for SR transmission.

To overcome the above issue, in another embodiment it is proposed thateach SL HARQ feedback is associated with first available (i.e. notassociated with any other HARQ feedback and present after the location(in time) of HARQ feedback) SR resource for SR configuration forrequesting HARQ retransmission.

FIG. 21 illustrates the timeline of an operation for requesting SL grantfor retransmission according to an embodiment of the disclosure.

Referring to FIG. 21 , HARQ feedback for transmission based on SL grant1 is associated with SR resource R3. HARQ feedback for transmissionbased on SL grant 2 is associated with SR resource R4. Note that SRresource R3 occurs in time after HARQ feedback for transmission based onSL grant 2 but is not available as it is associated with HARQ feedbackfor transmission based on SL grant 1. So, upon receiving HARQ-NACK fortransmission based on SL grant 2, UE transmits SR in SR resource R4.

To overcome the above issue in another embodiment, it is proposed thatinterval between SL grants is at least greater than or equal toperiodicity of SR resource in SR configuration for requesting HARQretransmission. Upon receiving SL HARQ-NACK, UE transmits SR in earliestavailable SR resource from SR configuration for requesting HARQretransmission.

Method 2: In another method of the disclosure it is proposed, uponreceiving sidelink HARQ-NACK, UE sends MAC control element (CE) to gNBfor requesting SL grant for HARQ retransmission.

FIG. 22 illustrates the timeline of an operation for requesting SL grantfor retransmission according to an embodiment of the disclosure.

MAC CE includes SL grant index (grant index is included in DCIscheduling SL grant), or MAC CE includes system frame number(SFN)/slot/symbol of SL grant corresponding to which UE is requestingtransmission. MAC CE can include request for retransmission for multipleSL grants.

Referring to FIG. 22 , HARQ-NACK is received for transmissioncorresponding to grant index 2, so UE transmits MAC CE including grantindex 2.

Method 3: In another method of the disclosure, it is proposed that gNBconfigures both mode 1 (i.e. dedicated resources) and mode 2 resources(common TX resources, resource selection based on sensing) to UE. Uponreceiving sidelink HARQ-NACK for transmission based on mode 1 grant, UEselects resource from mode 2 resource pool for HARQ retransmission. Inanother embodiment, upon receiving sidelink HARQ-NACK for transmissionbased on mode 1 grant, UE selects resource from mode 2 resource pool ifit fails to receive mode 1 SL grant within a (pre-) configured time.

Method 4: In another method of the disclosure, it is proposed that gNBautonomously provides SL grants for HARQ retransmission. gNB configuresSR resource(s) for stopping SL grant for HARQ retransmission. SRconfiguration(s) to be used for stopping SL grant for HARQretransmission are linked to grant index. gNB indicates which SRconfiguration(s) is for which grant index(s). Upon receiving sidelinkHARQ-ACK for HARQ transmission corresponding to a SL grant with grantindex x, UE transmit SR in SR resource of SR configuration correspondingto grant index x.

FIG. 23 illustrates the timeline of an operation for requesting SL grantfor retransmission according to an embodiment of the disclosure.

Referring to FIG. 23 , HARQ-ACK is received for transmissioncorresponding to grant index 1, so UE transmits SR in SR resource of SRconfiguration corresponding to grant index 1.

In an alternate embodiment, upon receiving sidelink HARQ-ACK, UE sendsMAC CE to gNB for stopping SL grant for HARQ retransmission. MAC CEincludes SL grant index, or MAC CE includes SFN/slot/symbol of SL grantcorresponding to which UE is requesting to stop giving grants forretransmission.

FIG. 24 illustrates the timeline of an operation for requesting SL grantfor retransmission according to an embodiment of the disclosure.

Referring to FIG. 24 , HARQ-ACK is received for transmissioncorresponding to grant index 1, so UE transmits MAC CE including grantindex 1.

It is to be noted that above methods can also be used for mode 1configured grants for sidelink. Instead of grant index, configured grantconfiguration index is used. Each configured grant configuration isassociated with index. It can be explicitly signaled, or it is the indexof entry in configuration list.

SL RBs/LCHs and SL RB Configurations for NR Sidelink

For SL unicast, groupcast and broadcast, QoS parameters of V2X packetsare instructed by the upper layers to the access stratum (AS).

Unicast Communication: In the transmitter, upper layers map thepacket(s) to PC5 QoS flow(s) via PC5 QoS rules, and pass the packet(s)down to the AS with associated QoS flow identifier(s) (i.e. PC5 QoS flowidentifier (QFI)). AS obtains SL radio bearer (SLRB) configurations viagNB/ng-eNB or via pre-configuration. These SLRB configurations includePC5 QoS flow to SLRB mapping, service data adaptation protocol(SDAP)/packet data convergence protocol (PDCP)/radio link control(RLC)/LCH configurations, etc. The UE in the AS establishes SLRB(s)associated with the PC5 QFI(s) of the packet(s), and maps availablepacket(s) to the SLRB(s) established.

Groupcast/Broadcast Communication: In the transmitter, the PC5 QoSprofile of each arriving V2X packet are set by the upper layers andsubmitted to the AS. AS obtains SLRB configurations via gNB/ng-eNB orvia pre-configuration. These SLRB configurations may include PC5 QoSprofile to SLRB mapping, PDCP/RLC/LCH configurations, etc. The UE in theAS establishes SLRB(s) associated with the QoS profile of the packet(s),and maps the packet(s) to the SLRB(s) established.

For SL unicast, the mapping between PC5 QoS flows and SLRBconfigurations is at least gNB configured via dedicated signaling orpre-configured. Similarly, for SL groupcast/broadcast, the mappingbetween PC5 QoS profile and SLRB configurations is at least gNBconfigured via dedicated signaling or pre-configured.

In an embodiment, for a UE in RRC IDLE/INACTIVE state, if the SIbroadcasted by the camped cell provides transmission resources forfrequency on which the UE is configured to transmit V2X sidelink unicastcommunication and the mapping between PC5 QoS flows and SLRBconfigurations is not broadcasted in system information, UE uses thepre-configured mapping between PC5 QoS flows and SLRB configurations. Ifmapping between PC5 QoS flows and SLRB configurations is broadcasted insystem information, UE uses this mapping acquired from SI.

In another embodiment, for a UE in RRC IDLE/INACTIVE state, if the SIbroadcasted by the camped cell provides transmission resources forfrequency on which the UE is configured to transmit V2X sidelink unicastcommunication and the mapping between PC5 QoS flows and SLRBconfigurations is not broadcasted in system information, UE initiatesthe RRC connection. After initiating the connection, UE obtains themapping between PC5 QoS flows and SLRB configurations from gNB indedicated signaling. If mapping between PC5 QoS flows and SLRBconfigurations is broadcasted in system information, UE uses thismapping acquired from SI.

For unicast/groupcast communication, SL RB configurations can bepre-configured or configured by gNB using dedicated RRC signaling or viasystem information. It is assumed that transmitter can provide the SL RBconfiguration(s) to the receiver(s) during the connection setup.

Scenario: UE is in RRC_CONNECTED state.

For a communication type (e.g. unicast), packets arrive fordestination 1. In the transmitter, upper layers map the packet(s) to PC5QoS flow X and pass the packet(s) down to the AS with associated QoSflow identifier(s) (i.e. PC5 QFI X).

AS sends SLRB configuration request to gNB.

gNB provides SLRB configuration 1. The SLRB configuration 1 is mapped toPC5 QFI X and includes SDAP/PDCP/RLC/LCH configurations, etc.

The UE in the AS establishes SLRB 1 associated with the PC5 QFI X fordestination 1 based on SLRB configuration 1. Packets of PC5 QFI X fordestination 1 are mapped to this SL RB.

Sometime later, for unicast communication packets arrive for destination2. In the transmitter, upper layers map the packet(s) to PC5 QoS flow Xbased on QoS rules and pass the packet(s) down to the AS with associatedQoS flow identifier(s) (i.e. PC5 QFI X).

In this scenario, there are two options:

Option 1: UE sends SLRB configuration request to gNB includingdestination ID and PC5 QFI. gNB provides SL RB configuration 2. The SLRBconfiguration 2 is mapped to PC5 QFI X and includes SDAP/PDCP/RLC/LCHconfigurations, etc. The UE in the AS establishes SLRB associated withthe PC5 QFI X for destination 2 based on SLRB configuration 2.

Option 2: UE does not send SLRB configuration request to gNB. The UE inthe AS establishes SLRB 2 associated with the PC5 QFI X for destination2 based on SLRB configuration 1. Packets of PC5 QFI X for destination 2are mapped to this SL RB. For a given communication type (e.g. unicast,groupcast), upon receiving the first packet of a PC5 QoS flow/QoSprofile from upper layer for a destination, if UE has SLRB configurationcorresponding to that PC5 QoS flow/QoS profile and communication type,UE establishes a new SLRB using the SLRB configuration corresponding tothat PC5 QoS flow/QoS profile and communication type. Otherwise, UEsends SLRB configuration request to gNB.

FIGS. 25 and 26 are the signaling flows between UE and gNB for acquiringV2X SIB(s) according to various embodiments of the disclosure.

In NR, SI framework whether an SI message is broadcasted or provided ondemand is up to network implementation. Whether SI message is beingbroadcasted or provided on demand is indicated in SIB1. If SI messageincluding the V2X SIB(s) is not being broadcasted (i.e. provided ondemand), RRC_CONNECTED UE acquires V2X SIB(s).

Referring to FIG. 25 , UE is in RRC_CONNECTED and needs to acquire V2XSIB(s) which are not being broadcasted. The UE transmits anRRCSystemInfoRequest message to gNB at operation 2510. TheRRCSystemInfoRequest message is transmitted over dedicated controlchannel (DCCH). The RRCSystemInfoRequest includes request for SImessage(s) which are associated with V2X SIBs or includes request forV2X SIB(s). Mapping between V2X SIBs and SI messages is indicated inSIB1. The gNB transmits an RRC reconfiguration message to the UE atoperation 2520. The RRC reconfiguration message includes the requestedV2X SIB(s) or SI message(s). gNB may also broadcast SI message(s)including the requested V2X SIB(s) in SI windows. So, after transmittingRRCSystemInfoRequest in RRC_connected state, UE also monitors SI windowscorresponding to the requested SI messages or corresponding to SImessages of the requested V2X SIB(s).

In case of embodiment based on FIG. 25 , after initiating transmissionof RRCSystemInfoRequest, UE waits for acknowledgment for SI request onlyif UE is in RRC IDLE/INACTIVE state. UE does not wait for acknowledgmentfor SI request if UE is in RRC_CONNECTED state. RRCSystemInfoRequest inRRC_IDLE/INACTIVE is transmitted over common control channel (CCCH) andincludes request for SI message(s) which are associated with V2X SIBs.Upon transmitting RRCSystemInfoRequest over CCCH, UE receives therequested SI messages in corresponding SI windows.

Referring to FIG. 26 , UE is in RRC_CONNECTED and needs to acquire V2XSIB(s) which are not being broadcasted. The UE transmits anRRCSystemInfoRequest message to gNB at operation 2610. The gNB transmitsan RRCSystemInfoRequest ACK to the UE at operation 2620. The UE monitorsSI window(s) of requested SI message in current modification period atoperation 2630.

In case of embodiment based on FIG. 26 , after initiating transmissionof RRCSystemInfoRequest, UE waits for acknowledgment for SI request fromlower layers (contention resolution MAC CE acts as SI request ACK) if UEis in RRC_IDLE/INACTIVE state. RRCSystemInfoRequest is transmitted byIDLE/INACTIVE UE using CCCH. After receiving RRCSystemInfoRequest inmessage 3 (Msg3) in CCCH SDU, gNB transmits contention resolution MAC CEacknowledging reception of SI request. If UE is in RRC_CONNECTED state,it waits for RRCSystemInfoRequest ACK message. RRCSystemInfoRequest istransmitted by RRC_CONNECTED UE using DCCH. After receivingRRCSystemInfoRequest in DCCH, gNB transmits RRCSystemInfoRequestAckacknowledging reception of SI request.

In an embodiment of FIG. 25 , UE can start a timer upon initiatingtransmission of RRCSystemInfoRequest. Timer is stopped upon receivingRRCReconfiguration message including requested SI. If timer expires UEinitiate transmission of RRCSystemInfoRequest again. Upon failure toreceive desired SI after transmitting RRCSystemInfoRequest for ‘N’times, UE may declare radio link failure (RLF). N can be configured inSI or dedicated signaling or pre-defined.

FIG. 27 is a block diagram of a terminal according to an embodiment ofthe disclosure.

Referring to FIG. 27 , a terminal includes a transceiver 2710, acontroller 2720 and a memory 2730. The controller 2720 may refer to acircuitry, an ASIC, an FPGA, or at least one processor. The transceiver2710, the controller 2720 and the memory 2730 are configured to performthe operations of the UE illustrated in the figures, e.g. FIGS. 1 to 26, or as otherwise described above. Although the transceiver 2710, thecontroller 2720 and the memory 2730 are shown as separate entities, theymay be integrated onto a single chip. The transceiver 2710, thecontroller 2720 and the memory 2730 may also be electrically connectedto or coupled with each other.

The transceiver 2710 may transmit and receive signals to and from othernetwork entities, e.g., a base station.

The controller 2720 may control the UE to perform functions according tothe embodiments described above. For example, the controller 2720 isconfigured to control the transceiver 2710 to receive system informationincluding sidelink communication information of second RAT. In ascenario, UE is camped on a cell of first RAT (i.e. NR) but interestedin sidelink communication based on second RAT (i.e. LTE) on the campedfrequency. The controller 2720 is configured to initiate an RRCconnection on the camped cell of the first RAT for sidelinkcommunication according to second RAT: if the frequency on which the UEis configured to transmit sidelink communication according to second RATconcerns the camped frequency; and if the system information broadcastedby the camped cell of first RAT does not include transmission resourcesfor sidelink communication according to second RAT. In another scenario,UE is camped on a cell of first RAT (i.e. NR) but interested in sidelinkcommunication based on second RAT (i.e. LTE) on frequency other than thecamped frequency. The controller 2720 is configured to initiate an RRCconnection on the camped cell of the first RAT for sidelinkcommunication according to second RAT: if the frequency on which the UEis configured to transmit sidelink communication according to second RATis included in system information broadcasted by the camped cell offirst RAT and does not include transmission resource pool for sidelinkcommunication according to second RAT for that frequency. The controller2720 is configured to control the transceiver 2710 to transmit asidelink UE information message for sidelink communication according tosecond RAT to camped cell of first RAT. The controller 2720 isconfigured to control the transceiver 2710 to receive information onresources for sidelink communication according to second RAT in thededicated signaling. In another scenario, the first RAT may refer to LTEand the second RAT may refer to NR.

In an embodiment, the operations of the terminal may be implementedusing the memory 2730 storing corresponding program codes. Specifically,the terminal may be equipped with the memory 2730 to store program codesimplementing desired operations. To perform the desired operations, thecontroller 2720 may read and execute the program codes stored in thememory 2730 by using a processor or a central processing unit (CPU).

FIG. 28 is a block diagram of a base station according to an embodimentof the disclosure.

Referring to FIG. 28 , a base station includes a transceiver 2810, acontroller 2820 and a memory 2830. The controller 2820 may refer to acircuitry, an ASIC, an FPGA, or at least one processor. The transceiver2810, the controller 2820 and the memory 2830 are configured to performthe operations of the gNB illustrated in the figures, e.g. FIGS. 1 to 26, or as otherwise described above. Although the transceiver 2810, thecontroller 2820 and the memory 2830 are shown as separate entities, theymay be integrated onto a single chip. The transceiver 2810, thecontroller 2820 and the memory 2830 may also be electrically connectedto or coupled with each other.

The transceiver 2810 may transmit and receive signals to and from othernetwork entities, e.g., a terminal.

The controller 2820 may control the gNB to perform functions accordingto the embodiments described above. For example, the controller 2820 isconfigured to control the transceiver 2810 to broadcast systeminformation including sidelink communication information of second RAT.The controller 2820 is configured to control the transceiver 2810 toreceive a sidelink UE information message for sidelink communicationaccording to second RAT to camped cell of first RAT. The controller 2820is configured to control the transceiver 2810 to provide resources forsidelink communication according to second RAT in dedicated signaling.

In an embodiment, the operations of the base station may be implementedusing the memory 2830 storing corresponding program codes. Specifically,the base station may be equipped with the memory 2830 to store programcodes implementing desired operations. To perform the desiredoperations, the controller 2820 may read and execute the program codesstored in the memory 2830 by using a processor or a CPU.

While the disclosure has been shown and described with reference tovarious embodiments thereof, it will be understood by those skilled inthe art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the disclosure as definedby the appended claims and their equivalents.

What is claimed is:
 1. A method performed by a user equipment (UE) in awireless communication system, the method comprising: receiving, from abase station associated with a first radio access technology (RAT), asystem information block containing configuration information for asidelink communication according to a second RAT; in case that afrequency on which the UE is configured to transmit a sidelink signalaccording to the second RAT is included in an inter frequencyinformation list within the configuration information, identifyingwhether the configuration information includes transmission resourcesfor the sidelink signal according to the second RAT; and in case thatthe configuration information does not include the transmissionresources for the sidelink signal according to the second RAT,performing a radio resource control (RRC) connection for the sidelinkcommunication according to the second RAT.
 2. The method of claim 1,further comprising: transmitting, to the base station, a sidelink UEinformation message for the sidelink communication according to thesecond RAT; and receiving, from the base station, an RRC reconfigurationmessage including the transmission resources for the sidelink signalaccording to the second RAT.
 3. The method of claim 2, furthercomprising transmitting, to another UE, the sidelink signal according tothe second RAT based on the transmission resources.
 4. The method ofclaim 1, wherein the first RAT corresponds to a long term evolution(LTE) communication and the second RAT corresponds to a new radio (NR)communication system.
 5. The method of claim 1, wherein the first RATcorresponds to a new radio (NR) communication system and the second RATcorresponds to a long term evolution (LTE) communication system.
 6. Auser equipment (UE) in a wireless communication system, the UEcomprising: a transceiver; and at least one processor operativelycoupled with the transceiver and configured to: control the transceiverto receive, from a base station associated with a first radio accesstechnology (RAT), a system information block containing configurationinformation for a sidelink communication according to a second RAT, incase that a frequency on which the UE is configured to transmit asidelink signal according to the second RAT is included in an interfrequency information list within the configuration information,identify whether the configuration information includes transmissionresources for the sidelink signal according to the second RAT, and incase that the configuration information does not include thetransmission resources for the sidelink signal according to the secondRAT, perform a radio resource control (RRC) connection for the sidelinkcommunication according to the second RAT.
 7. The UE of claim 6, whereinthe at least one processor is further configured to: control thetransceiver to transmit, to the base station, a sidelink UE informationmessage for the sidelink communication according to the second RAT, andcontrol the transceiver to receive, from the base station, an RRCreconfiguration message including the transmission resources for thesidelink signal according to the second RAT.
 8. The UE of claim 7,wherein the at least one processor is further configured to control thetransceiver to transmit, to another UE, the sidelink signal according tothe second RAT based on the transmission resources.
 9. The UE of claim6, wherein the first RAT corresponds to a long term evolution (LTE)communication and the second RAT corresponds to a new radio (NR)communication system.
 10. The UE of claim 6, wherein the first RATcorresponds to a new radio (NR) communication system and the secondRAT-corresponds to a long term evolution (LTE) communication system. 11.A method performed by a base station associated with a first radioaccess technology (RAT) in a wireless communication system, the methodcomprising: transmitting system information block containingconfiguration information for a sidelink communication according to asecond RAT; and in case that a frequency on which a user equipment (UE)is configured to transmit a sidelink signal according to the second RATis included in an inter frequency information list within theconfiguration information, and the configuration information does notinclude transmission resources for the sidelink signal according to thesecond RAT, performing, with the UE, a radio resource control (RRC)connection for the sidelink communication according to the second RAT.12. The method of claim 11, further comprising: receiving, from the UE,a sidelink UE information message for the sidelink communicationaccording to the second RAT; and transmitting, to the UE, an RRCreconfiguration message including the transmission resources for thesidelink signal according to the second RAT.
 13. The method of claim 12,wherein the transmission resources are used to transmit the sidelinksignal according to the second RAT to another UE.
 14. The method ofclaim 11, wherein the first RAT corresponds to a long term evolution(LTE) communication system, and the second RAT corresponds to a newradio (NR) communication system.
 15. The method of claim 11, wherein thefirst RAT corresponds to a new radio (NR), communication system, and thesecond RAT corresponds to a long term evolution (LTE) communicationsystem.
 16. A base station associated with a first radio accesstechnology (RAT) in a wireless communication system, the base stationcomprising: a transceiver; and at least one processor operativelycoupled with the transceiver and configured to: control the transceiverto transmit a system information block containing configurationinformation for a sidelink communication according to a second RAT, andin case that a frequency on which a user equipment (UE) is configured totransmit a sidelink signal according to the second RAT is included in aninter frequency information list within the configuration information,and the configuration information does not include transmissionresources for the sidelink signal according to the second RAT, perform,with the UE, a radio resource control (RRC) connection for the sidelinkcommunication according to the second RAT.
 17. The base station of claim16, wherein the at least one processor is further configured to: controlthe transceiver to receive, from the UE, a sidelink UE informationmessage for the sidelink communication according to the second RAT, andcontrol the transceiver to transmit, to the UE, an RRC reconfigurationmessage including the transmission resources for the sidelink signalaccording to the second RAT.
 18. The base station of claim 17, whereinthe transmission resources are used to transmit the sidelink signalaccording to the second RAT to another UE.
 19. The base station of claim16, wherein the first RAT corresponds to a long term evolution (LTE)communication system, and the second RAT corresponds to a new radio (NR)communication system.
 20. The base station of claim 16, wherein thefirst RAT corresponds to a new radio (NR), communication system, and thesecond RAT corresponds to a long term evolution (LTE) communicationsystem.